role.go

/*
Copyright 2021 Gravitational, Inc.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package services

import (
	"context"
	"encoding/json"
	"fmt"
	"sort"
	"strings"
	"time"

	"github.com/google/uuid"
	"github.com/gravitational/configure/cstrings"
	"github.com/gravitational/trace"
	log "github.com/sirupsen/logrus"
	"github.com/vulcand/predicate"
	"golang.org/x/crypto/ssh"

	"github.com/zmb3/teleport"
	"github.com/zmb3/teleport/api/constants"
	"github.com/zmb3/teleport/api/defaults"
	"github.com/zmb3/teleport/api/types"
	"github.com/zmb3/teleport/api/types/wrappers"
	apiutils "github.com/zmb3/teleport/api/utils"
	"github.com/zmb3/teleport/api/utils/keys"
	"github.com/zmb3/teleport/lib/tlsca"
	"github.com/zmb3/teleport/lib/utils"
	"github.com/zmb3/teleport/lib/utils/parse"
)

// DefaultImplicitRules provides access to the default set of implicit rules
// assigned to all roles.
var DefaultImplicitRules = []types.Rule{
	types.NewRule(types.KindNode, RO()),
	types.NewRule(types.KindProxy, RO()),
	types.NewRule(types.KindAuthServer, RO()),
	types.NewRule(types.KindReverseTunnel, RO()),
	types.NewRule(types.KindCertAuthority, ReadNoSecrets()),
	types.NewRule(types.KindClusterAuthPreference, RO()),
	types.NewRule(types.KindClusterName, RO()),
	types.NewRule(types.KindSSHSession, RO()),
	types.NewRule(types.KindAppServer, RO()),
	types.NewRule(types.KindRemoteCluster, RO()),
	types.NewRule(types.KindKubeService, RO()),
	types.NewRule(types.KindKubeServer, RO()),
	types.NewRule(types.KindDatabaseServer, RO()),
	types.NewRule(types.KindDatabase, RO()),
	types.NewRule(types.KindApp, RO()),
	types.NewRule(types.KindWindowsDesktopService, RO()),
	types.NewRule(types.KindWindowsDesktop, RO()),
	types.NewRule(types.KindKubernetesCluster, RO()),
	types.NewRule(types.KindUsageEvent, []string{types.VerbCreate}),
}

// DefaultCertAuthorityRules provides access the minimal set of resources
// needed for a certificate authority to function.
var DefaultCertAuthorityRules = []types.Rule{
	types.NewRule(types.KindSession, RO()),
	types.NewRule(types.KindNode, RO()),
	types.NewRule(types.KindAuthServer, RO()),
	types.NewRule(types.KindReverseTunnel, RO()),
	types.NewRule(types.KindCertAuthority, ReadNoSecrets()),
}

// ErrSessionMFARequired is returned by AccessChecker when access to a resource
// requires an MFA check.
var ErrSessionMFARequired = trace.AccessDenied("access to resource requires MFA")

// RoleNameForUser returns role name associated with a user.
func RoleNameForUser(name string) string {
	return "user:" + name
}

// RoleNameForCertAuthority returns role name associated with a certificate
// authority.
func RoleNameForCertAuthority(name string) string {
	return "ca:" + name
}

// NewImplicitRole is the default implicit role that gets added to all
// RoleSets.
func NewImplicitRole() types.Role {
	return &types.RoleV5{
		Kind:    types.KindRole,
		Version: types.V3,
		Metadata: types.Metadata{
			Name:      constants.DefaultImplicitRole,
			Namespace: defaults.Namespace,
		},
		Spec: types.RoleSpecV5{
			Options: types.RoleOptions{
				MaxSessionTTL: types.MaxDuration(),
				// Explicitly disable options that default to true, otherwise the option
				// will always be enabled, as this implicit role is part of every role set.
				PortForwarding: types.NewBoolOption(false),
				RecordSession: &types.RecordSession{
					Desktop: types.NewBoolOption(false),
				},
			},
			Allow: types.RoleConditions{
				Namespaces: []string{defaults.Namespace},
				Rules:      types.CopyRulesSlice(DefaultImplicitRules),
			},
		},
	}
}

// RoleForUser creates an admin role for a services.User.
//
// Used in tests only.
func RoleForUser(u types.User) types.Role {
	role, _ := types.NewRole(RoleNameForUser(u.GetName()), types.RoleSpecV5{
		Options: types.RoleOptions{
			CertificateFormat: constants.CertificateFormatStandard,
			MaxSessionTTL:     types.NewDuration(defaults.MaxCertDuration),
			PortForwarding:    types.NewBoolOption(true),
			ForwardAgent:      types.NewBool(true),
			BPF:               defaults.EnhancedEvents(),
		},
		Allow: types.RoleConditions{
			Namespaces:       []string{defaults.Namespace},
			NodeLabels:       types.Labels{types.Wildcard: []string{types.Wildcard}},
			AppLabels:        types.Labels{types.Wildcard: []string{types.Wildcard}},
			KubernetesLabels: types.Labels{types.Wildcard: []string{types.Wildcard}},
			DatabaseLabels:   types.Labels{types.Wildcard: []string{types.Wildcard}},
			Rules: []types.Rule{
				types.NewRule(types.KindRole, RW()),
				types.NewRule(types.KindAuthConnector, RW()),
				types.NewRule(types.KindSession, RO()),
				types.NewRule(types.KindTrustedCluster, RW()),
				types.NewRule(types.KindEvent, RO()),
				types.NewRule(types.KindClusterAuthPreference, RW()),
				types.NewRule(types.KindClusterNetworkingConfig, RW()),
				types.NewRule(types.KindSessionRecordingConfig, RW()),
				types.NewRule(types.KindApp, RW()),
				types.NewRule(types.KindDatabase, RW()),
				types.NewRule(types.KindLock, RW()),
				types.NewRule(types.KindToken, RW()),
				types.NewRule(types.KindConnectionDiagnostic, RW()),
				types.NewRule(types.KindKubernetesCluster, RW()),
				types.NewRule(types.KindSessionTracker, RO()),
			},
			JoinSessions: []*types.SessionJoinPolicy{
				{
					Name:  "foo",
					Roles: []string{"*"},
					Kinds: []string{string(types.SSHSessionKind)},
					Modes: []string{string(types.SessionPeerMode)},
				},
			},
		},
	})
	return role
}

// RoleForCertAuthority creates role using types.CertAuthority.
func RoleForCertAuthority(ca types.CertAuthority) types.Role {
	role, _ := types.NewRole(RoleNameForCertAuthority(ca.GetClusterName()), types.RoleSpecV5{
		Options: types.RoleOptions{
			MaxSessionTTL: types.NewDuration(defaults.MaxCertDuration),
		},
		Allow: types.RoleConditions{
			Namespaces:       []string{defaults.Namespace},
			NodeLabels:       types.Labels{types.Wildcard: []string{types.Wildcard}},
			AppLabels:        types.Labels{types.Wildcard: []string{types.Wildcard}},
			KubernetesLabels: types.Labels{types.Wildcard: []string{types.Wildcard}},
			DatabaseLabels:   types.Labels{types.Wildcard: []string{types.Wildcard}},
			Rules:            types.CopyRulesSlice(DefaultCertAuthorityRules),
		},
	})
	return role
}

// ValidateRoleName checks that the role name is allowed to be created.
func ValidateRoleName(role types.Role) error {
	// System role names are not allowed.
	systemRoles := types.SystemRoles([]types.SystemRole{
		types.SystemRole(role.GetMetadata().Name),
	})
	if err := systemRoles.Check(); err == nil {
		return trace.BadParameter("reserved role: %s", role.GetMetadata().Name)
	}
	return nil
}

// ValidateRole parses validates the role, and sets default values.
func ValidateRole(r types.Role) error {
	if err := r.CheckAndSetDefaults(); err != nil {
		return err
	}

	// if we find {{ or }} but the syntax is invalid, the role is invalid
	for _, condition := range []types.RoleConditionType{types.Allow, types.Deny} {
		for _, login := range r.GetLogins(condition) {
			if strings.Contains(login, "{{") || strings.Contains(login, "}}") {
				_, err := parse.NewExpression(login)
				if err != nil {
					return trace.BadParameter("invalid login found: %v", login)
				}
			}
		}
	}

	rules := append(r.GetRules(types.Allow), r.GetRules(types.Deny)...)
	for _, rule := range rules {
		if err := validateRule(rule); err != nil {
			return trace.Wrap(err)
		}
	}

	return nil
}

// validateRule parses the where and action fields to validate the rule.
func validateRule(r types.Rule) error {
	if len(r.Where) != 0 {
		parser, err := NewWhereParser(&Context{})
		if err != nil {
			return trace.Wrap(err)
		}
		_, err = parser.Parse(r.Where)
		if err != nil {
			return trace.BadParameter("could not parse 'where' rule: %q, error: %v", r.Where, err)
		}
	}

	if len(r.Actions) != 0 {
		parser, err := NewActionsParser(&Context{})
		if err != nil {
			return trace.Wrap(err)
		}
		for i, action := range r.Actions {
			_, err = parser.Parse(action)
			if err != nil {
				return trace.BadParameter("could not parse action %v %q, error: %v", i, action, err)
			}
		}
	}
	return nil
}

func filterInvalidUnixLogins(candidates []string) []string {
	// The tests for `ApplyTraits()` require that an empty list is nil
	// rather than a 0-size slice, and I don't understand the potential
	// knock-on effects of changing that, so the  default value is `nil`
	output := []string(nil)

	for _, candidate := range candidates {
		if !cstrings.IsValidUnixUser(candidate) {
			log.Debugf("Skipping login %v, not a valid Unix login.", candidate)
			continue
		}

		// A valid variable was found in the traits, append it to the list of logins.
		output = append(output, candidate)
	}
	return output
}

func filterInvalidWindowsLogins(candidates []string) []string {
	var output []string

	// https://docs.microsoft.com/en-us/previous-versions/windows/it-pro/windows-2000-server/bb726984(v=technet.10)
	const invalidChars = `"/\[]:;|=,+*?<>`

	for _, candidate := range candidates {
		if strings.ContainsAny(candidate, invalidChars) {
			log.Debugf("Skipping Windows login %v, not a valid Windows login.", candidate)
			continue
		}

		output = append(output, candidate)
	}

	return output
}

// ApplyTraits applies the passed in traits to any variables within the role
// and returns itself.
func ApplyTraits(r types.Role, traits map[string][]string) types.Role {
	for _, condition := range []types.RoleConditionType{types.Allow, types.Deny} {
		inLogins := r.GetLogins(condition)
		outLogins := applyValueTraitsSlice(inLogins, traits, "login")
		outLogins = filterInvalidUnixLogins(outLogins)
		r.SetLogins(condition, apiutils.Deduplicate(outLogins))

		inWindowsLogins := r.GetWindowsLogins(condition)
		outWindowsLogins := applyValueTraitsSlice(inWindowsLogins, traits, "windows_login")
		outWindowsLogins = filterInvalidWindowsLogins(outWindowsLogins)
		r.SetWindowsLogins(condition, apiutils.Deduplicate(outWindowsLogins))

		inRoleARNs := r.GetAWSRoleARNs(condition)
		outRoleARNs := applyValueTraitsSlice(inRoleARNs, traits, "AWS role ARN")
		r.SetAWSRoleARNs(condition, apiutils.Deduplicate(outRoleARNs))

		// apply templates to kubernetes groups
		inKubeGroups := r.GetKubeGroups(condition)
		outKubeGroups := applyValueTraitsSlice(inKubeGroups, traits, "kube group")
		r.SetKubeGroups(condition, apiutils.Deduplicate(outKubeGroups))

		// apply templates to kubernetes users
		inKubeUsers := r.GetKubeUsers(condition)
		outKubeUsers := applyValueTraitsSlice(inKubeUsers, traits, "kube user")
		r.SetKubeUsers(condition, apiutils.Deduplicate(outKubeUsers))

		// apply templates to database names
		inDbNames := r.GetDatabaseNames(condition)
		outDbNames := applyValueTraitsSlice(inDbNames, traits, "database name")
		r.SetDatabaseNames(condition, apiutils.Deduplicate(outDbNames))

		// apply templates to database users
		inDbUsers := r.GetDatabaseUsers(condition)
		outDbUsers := applyValueTraitsSlice(inDbUsers, traits, "database user")
		r.SetDatabaseUsers(condition, apiutils.Deduplicate(outDbUsers))

		// apply templates to node labels
		inLabels := r.GetNodeLabels(condition)
		if inLabels != nil {
			r.SetNodeLabels(condition, applyLabelsTraits(inLabels, traits))
		}

		// apply templates to cluster labels
		inLabels = r.GetClusterLabels(condition)
		if inLabels != nil {
			r.SetClusterLabels(condition, applyLabelsTraits(inLabels, traits))
		}

		// apply templates to kube labels
		inLabels = r.GetKubernetesLabels(condition)
		if inLabels != nil {
			r.SetKubernetesLabels(condition, applyLabelsTraits(inLabels, traits))
		}

		// apply templates to app labels
		inLabels = r.GetAppLabels(condition)
		if inLabels != nil {
			r.SetAppLabels(condition, applyLabelsTraits(inLabels, traits))
		}

		// apply templates to database labels
		inLabels = r.GetDatabaseLabels(condition)
		if inLabels != nil {
			r.SetDatabaseLabels(condition, applyLabelsTraits(inLabels, traits))
		}

		// apply templates to windows desktop labels
		inLabels = r.GetWindowsDesktopLabels(condition)
		if inLabels != nil {
			r.SetWindowsDesktopLabels(condition, applyLabelsTraits(inLabels, traits))
		}

		r.SetHostGroups(condition,
			applyValueTraitsSlice(r.GetHostGroups(condition), traits, "host_groups"))

		r.SetHostSudoers(condition,
			applyValueTraitsSlice(r.GetHostSudoers(condition), traits, "host_sudoers"))

		options := r.GetOptions()
		for i, ext := range options.CertExtensions {
			vals, err := ApplyValueTraits(ext.Value, traits)
			if err != nil && !trace.IsNotFound(err) {
				log.Warnf("Did not apply trait to cert_extensions.value: %v", err)
				continue
			}
			if len(vals) != 0 {
				options.CertExtensions[i].Value = vals[0]
			}
		}

		// apply templates to impersonation conditions
		inCond := r.GetImpersonateConditions(condition)
		var outCond types.ImpersonateConditions
		outCond.Users = applyValueTraitsSlice(inCond.Users, traits, "impersonate user")
		outCond.Roles = applyValueTraitsSlice(inCond.Roles, traits, "impersonate role")
		outCond.Users = apiutils.Deduplicate(outCond.Users)
		outCond.Roles = apiutils.Deduplicate(outCond.Roles)
		outCond.Where = inCond.Where
		r.SetImpersonateConditions(condition, outCond)
	}

	return r
}

// applyValueTraitsSlice iterates over a slice of input strings, calling
// ApplyValueTraits on each.
func applyValueTraitsSlice(inputs []string, traits map[string][]string, fieldName string) []string {
	var output []string
	for _, value := range inputs {
		outputs, err := ApplyValueTraits(value, traits)
		if err != nil {
			if !trace.IsNotFound(err) {
				log.WithError(err).Debugf("Skipping %s %q.", fieldName, value)
			}
			continue
		}
		output = append(output, outputs...)
	}
	return output
}

// applyLabelsTraits interpolates variables based on the templates
// and traits from identity provider. For example:
//
// cluster_labels:
//
//	env: ['{{external.groups}}']
//
// and groups: ['admins', 'devs']
//
// will be interpolated to:
//
// cluster_labels:
//
//	env: ['admins', 'devs']
func applyLabelsTraits(inLabels types.Labels, traits map[string][]string) types.Labels {
	outLabels := make(types.Labels, len(inLabels))
	// every key will be mapped to the first value
	for key, vals := range inLabels {
		keyVars, err := ApplyValueTraits(key, traits)
		if err != nil {
			// empty key will not match anything
			log.Debugf("Setting empty node label pair %q -> %q: %v", key, vals, err)
			keyVars = []string{""}
		}

		var values []string
		for _, val := range vals {
			valVars, err := ApplyValueTraits(val, traits)
			if err != nil {
				log.Debugf("Setting empty node label value %q -> %q: %v", key, val, err)
				// empty value will not match anything
				valVars = []string{""}
			}
			values = append(values, valVars...)
		}
		outLabels[keyVars[0]] = apiutils.Deduplicate(values)
	}
	return outLabels
}

// ApplyValueTraits applies the passed in traits to the variable,
// returns BadParameter in case if referenced variable is unsupported,
// returns NotFound in case if referenced trait is missing,
// mapped list of values otherwise, the function guarantees to return
// at least one value in case if return value is nil
func ApplyValueTraits(val string, traits map[string][]string) ([]string, error) {
	// Extract the variable from the role variable.
	variable, err := parse.NewExpression(val)
	if err != nil {
		return nil, trace.Wrap(err)
	}

	// verify that internal traits match the supported variables
	if variable.Namespace() == teleport.TraitInternalPrefix {
		switch variable.Name() {
		case constants.TraitLogins, constants.TraitWindowsLogins,
			constants.TraitKubeGroups, constants.TraitKubeUsers,
			constants.TraitDBNames, constants.TraitDBUsers,
			constants.TraitAWSRoleARNs, teleport.TraitJWT:
		default:
			return nil, trace.BadParameter("unsupported variable %q", variable.Name())
		}
	}

	// If the variable is not found in the traits, skip it.
	interpolated, err := variable.Interpolate(traits)
	if trace.IsNotFound(err) || len(interpolated) == 0 {
		return nil, trace.NotFound("variable %q not found in traits", variable.Name())
	}
	if err != nil {
		return nil, trace.Wrap(err)
	}
	return interpolated, nil
}

// ruleScore is a sorting score of the rule, the larger the score, the more
// specific the rule is
func ruleScore(r *types.Rule) int {
	score := 0
	// wildcard rules are less specific
	if apiutils.SliceContainsStr(r.Resources, types.Wildcard) {
		score -= 4
	} else if len(r.Resources) == 1 {
		// rules that match specific resource are more specific than
		// fields that match several resources
		score += 2
	}
	// rules that have wildcard verbs are less specific
	if apiutils.SliceContainsStr(r.Verbs, types.Wildcard) {
		score -= 2
	}
	// rules that supply 'where' or 'actions' are more specific
	// having 'where' or 'actions' is more important than
	// whether the rules are wildcard or not, so here we have +8 vs
	// -4 and -2 score penalty for wildcards in resources and verbs
	if len(r.Where) > 0 {
		score += 8
	}
	// rules featuring actions are more specific
	if len(r.Actions) > 0 {
		score += 8
	}
	return score
}

// CompareRuleScore returns true if the first rule is more specific than the other.
//
// * nRule matching wildcard resource is less specific
// than same rule matching specific resource.
// * Rule that has wildcard verbs is less specific
// than the same rules matching specific verb.
// * Rule that has where section is more specific
// than the same rule without where section.
// * Rule that has actions list is more specific than
// rule without actions list.
func CompareRuleScore(r *types.Rule, o *types.Rule) bool {
	return ruleScore(r) > ruleScore(o)
}

// RuleSet maps resource to a set of rules defined for it
type RuleSet map[string][]types.Rule

// MakeRuleSet creates a new rule set from a list
func MakeRuleSet(rules []types.Rule) RuleSet {
	set := make(RuleSet)
	for _, rule := range rules {
		for _, resource := range rule.Resources {
			set[resource] = append(set[resource], rule)
		}
	}
	for resource := range set {
		rules := set[resource]
		// sort rules by most specific rule, the rule that has actions
		// is more specific than the one that has no actions
		sort.Slice(rules, func(i, j int) bool {
			return CompareRuleScore(&rules[i], &rules[j])
		})
		set[resource] = rules
	}
	return set
}

// Match tests if the resource name and verb are in a given list of rules.
// More specific rules will be matched first. See Rule.IsMoreSpecificThan
// for exact specs on whether the rule is more or less specific.
//
// Specifying order solves the problem on having multiple rules, e.g. one wildcard
// rule can override more specific rules with 'where' sections that can have
// 'actions' lists with side effects that will not be triggered otherwise.
func (set RuleSet) Match(whereParser predicate.Parser, actionsParser predicate.Parser, resource string, verb string) (bool, error) {
	// empty set matches nothing
	if len(set) == 0 {
		return false, nil
	}

	// check for matching resource by name
	// the most specific rule should win
	rules := set[resource]
	for _, rule := range rules {
		match, err := matchesWhere(&rule, whereParser)
		if err != nil {
			return false, trace.Wrap(err)
		}
		if match && (rule.HasVerb(types.Wildcard) || rule.HasVerb(verb)) {
			if err := processActions(&rule, actionsParser); err != nil {
				return true, trace.Wrap(err)
			}
			return true, nil
		}
	}

	// check for wildcard resource matcher
	for _, rule := range set[types.Wildcard] {
		match, err := matchesWhere(&rule, whereParser)
		if err != nil {
			return false, trace.Wrap(err)
		}
		if match && (rule.HasVerb(types.Wildcard) || rule.HasVerb(verb)) {
			if err := processActions(&rule, actionsParser); err != nil {
				return true, trace.Wrap(err)
			}
			return true, nil
		}
	}

	return false, nil
}

// matchesWhere returns true if Where rule matches.
// Empty Where block always matches.
func matchesWhere(r *types.Rule, parser predicate.Parser) (bool, error) {
	if r.Where == "" {
		return true, nil
	}
	ifn, err := parser.Parse(r.Where)
	if err != nil {
		return false, trace.Wrap(err)
	}
	fn, ok := ifn.(predicate.BoolPredicate)
	if !ok {
		return false, trace.BadParameter("invalid predicate type for where expression: %v", r.Where)
	}
	return fn(), nil
}

// processActions processes actions specified for this rule
func processActions(r *types.Rule, parser predicate.Parser) error {
	for _, action := range r.Actions {
		ifn, err := parser.Parse(action)
		if err != nil {
			return trace.Wrap(err)
		}
		fn, ok := ifn.(predicate.BoolPredicate)
		if !ok {
			return trace.BadParameter("invalid predicate type for action expression: %v", action)
		}
		fn()
	}
	return nil
}

// Slice returns slice from a set
func (set RuleSet) Slice() []types.Rule {
	var out []types.Rule
	for _, rules := range set {
		out = append(out, rules...)
	}
	return out
}

// HostUsersInfo keeps information about groups and sudoers entries
// for a particular host user
type HostUsersInfo struct {
	// Groups is the list of groups to include host users in
	Groups []string
	// Sudoers is a list of entries for a users sudoers file
	Sudoers []string
}

// RoleFromSpec returns new Role created from spec
func RoleFromSpec(name string, spec types.RoleSpecV5) (types.Role, error) {
	role, err := types.NewRole(name, spec)
	return role, trace.Wrap(err)
}

// RoleSetFromSpec returns a new RoleSet from spec
func RoleSetFromSpec(name string, spec types.RoleSpecV5) (RoleSet, error) {
	role, err := RoleFromSpec(name, spec)
	if err != nil {
		return nil, trace.Wrap(err)
	}
	return NewRoleSet(role), nil
}

// RW is a shortcut that returns all verbs.
func RW() []string {
	return []string{types.VerbList, types.VerbCreate, types.VerbRead, types.VerbUpdate, types.VerbDelete}
}

// RO is a shortcut that returns read only verbs that provide access to secrets.
func RO() []string {
	return []string{types.VerbList, types.VerbRead}
}

// ReadNoSecrets is a shortcut that returns read only verbs that do not
// provide access to secrets.
func ReadNoSecrets() []string {
	return []string{types.VerbList, types.VerbReadNoSecrets}
}

// RoleGetter is an interface that defines GetRole method
type RoleGetter interface {
	// GetRole returns role by name
	GetRole(ctx context.Context, name string) (types.Role, error)
}

// ExtractFromCertificate will extract roles and traits from a *ssh.Certificate.
func ExtractFromCertificate(cert *ssh.Certificate) ([]string, wrappers.Traits, error) {
	roles, err := ExtractRolesFromCert(cert)
	if err != nil {
		return nil, nil, trace.Wrap(err)
	}
	traits, err := ExtractTraitsFromCert(cert)
	if err != nil {
		return nil, nil, trace.Wrap(err)
	}

	return roles, traits, nil
}

// ExtractFromIdentity will extract roles and traits from the *x509.Certificate
// which Teleport passes along as a *tlsca.Identity. If roles and traits do not
// exist in the certificates, they are extracted from the backend.
func ExtractFromIdentity(access UserGetter, identity tlsca.Identity) ([]string, wrappers.Traits, error) {
	// Legacy certs are not encoded with roles or traits,
	// so we fallback to the traits and roles in the backend.
	// empty traits are a valid use case in standard certs,
	// so we only check for whether roles are empty.
	if len(identity.Groups) == 0 {
		u, err := access.GetUser(identity.Username, false)
		if err != nil {
			return nil, nil, trace.Wrap(err)
		}

		log.Warnf("Failed to find roles in x509 identity for %v. Fetching "+
			"from backend. If the identity provider allows username changes, this can "+
			"potentially allow an attacker to change the role of the existing user.",
			identity.Username)
		return u.GetRoles(), u.GetTraits(), nil
	}

	return identity.Groups, identity.Traits, nil
}

// FetchRoleList fetches roles by their names, applies the traits to role
// variables, and returns the list
func FetchRoleList(roleNames []string, access RoleGetter, traits map[string][]string) (RoleSet, error) {
	var roles []types.Role

	for _, roleName := range roleNames {
		role, err := access.GetRole(context.TODO(), roleName)
		if err != nil {
			return nil, trace.Wrap(err)
		}
		roles = append(roles, ApplyTraits(role, traits))
	}

	return roles, nil
}

// FetchRoles fetches roles by their names, applies the traits to role
// variables, and returns the RoleSet. Adds runtime roles like the default
// implicit role to RoleSet.
func FetchRoles(roleNames []string, access RoleGetter, traits map[string][]string) (RoleSet, error) {
	roles, err := FetchRoleList(roleNames, access, traits)
	if err != nil {
		return nil, trace.Wrap(err)
	}
	return NewRoleSet(roles...), nil
}

// CurrentUserRoleGetter limits the interface of auth.ClientI to methods needed by FetchAllClusterRoles.
type CurrentUserRoleGetter interface {
	GetCurrentUser(context.Context) (types.User, error)
	GetCurrentUserRoles(context.Context) ([]types.Role, error)
	RoleGetter
}

// FetchAllClusterRoles fetches all roles available to the user on the
// specified cluster, applies traits, and adds runtime roles like the default
// implicit role to RoleSet.
func FetchAllClusterRoles(ctx context.Context, access CurrentUserRoleGetter, defaultRoleNames []string, defaultTraits wrappers.Traits) (RoleSet, error) {
	user, err := access.GetCurrentUser(ctx)
	if err != nil {
		// DELETE IN 12.0.0
		if trace.IsNotImplemented(err) {
			// get the role definition for all roles of user.
			// this may only fail if the role which we are looking for does not exist, or we don't have access to it.
			// example scenario when this may happen:
			// 1. we have set of roles [foo bar] from profile.
			// 2. the cluster is remote and maps the [foo, bar] roles to single role [guest]
			// 3. the remote cluster doesn't implement GetCurrentUser(), so we have no way to learn of [guest].
			// 4. FetchRoles([foo bar], ..., ...) fails as [foo bar] does not exist on remote cluster.
			roleSet, err := FetchRoles(defaultRoleNames, access, defaultTraits)
			return roleSet, trace.Wrap(err)
		}
		return nil, trace.Wrap(err)
	}

	roles, err := access.GetCurrentUserRoles(ctx)
	if err != nil {
		// DELETE IN 12.0
		if trace.IsNotImplemented(err) {
			roleSet, err := FetchRoles(user.GetRoles(), access, user.GetTraits())
			return roleSet, trace.Wrap(err)
		}
		return nil, trace.Wrap(err)
	}

	for i := range roles {
		roles[i] = ApplyTraits(roles[i], user.GetTraits())
	}
	return NewRoleSet(roles...), nil
}

// ExtractRolesFromCert extracts roles from certificate metadata extensions.
func ExtractRolesFromCert(cert *ssh.Certificate) ([]string, error) {
	data, ok := cert.Extensions[teleport.CertExtensionTeleportRoles]
	if !ok {
		return nil, trace.NotFound("no roles found")
	}
	return UnmarshalCertRoles(data)
}

// ExtractTraitsFromCert extracts traits from the certificate extensions.
func ExtractTraitsFromCert(cert *ssh.Certificate) (wrappers.Traits, error) {
	rawTraits, ok := cert.Extensions[teleport.CertExtensionTeleportTraits]
	if !ok {
		return nil, trace.NotFound("no traits found")
	}
	var traits wrappers.Traits
	err := wrappers.UnmarshalTraits([]byte(rawTraits), &traits)
	if err != nil {
		return nil, trace.Wrap(err)
	}
	return traits, nil
}

func ExtractAllowedResourcesFromCert(cert *ssh.Certificate) ([]types.ResourceID, error) {
	allowedResourcesStr, ok := cert.Extensions[teleport.CertExtensionAllowedResources]
	if !ok {
		// if not present in the cert, there are no resource-based restrictions
		return nil, nil
	}
	allowedResources, err := types.ResourceIDsFromString(allowedResourcesStr)
	return allowedResources, trace.Wrap(err)
}

// NewRoleSet returns new RoleSet based on the roles
func NewRoleSet(roles ...types.Role) RoleSet {
	// unauthenticated Nop role should not have any privileges
	// by default, otherwise it is too permissive
	if len(roles) == 1 && roles[0].GetName() == string(types.RoleNop) {
		return roles
	}
	return append(roles, NewImplicitRole())
}

// RoleSet is a set of roles that implements access control functionality
type RoleSet []types.Role

// EnumerationResult is a result of enumerating a role set against some property, e.g. allowed names or logins.
type EnumerationResult struct {
	allowedDeniedMap map[string]bool
	wildcardAllowed  bool
	wildcardDenied   bool
}

func (result *EnumerationResult) filtered(value bool) []string {
	var filtered []string

	for entity, allow := range result.allowedDeniedMap {
		if allow == value {
			filtered = append(filtered, entity)
		}
	}

	sort.Strings(filtered)

	return filtered
}

// Denied returns all explicitly denied users.
func (result *EnumerationResult) Denied() []string {
	return result.filtered(false)
}

// Allowed returns all known allowed users.
func (result *EnumerationResult) Allowed() []string {
	if result.WildcardDenied() {
		return nil
	}
	return result.filtered(true)
}

// WildcardAllowed is true if there * username allowed for given rule set.
func (result *EnumerationResult) WildcardAllowed() bool {
	return result.wildcardAllowed && !result.wildcardDenied
}

// WildcardDenied is true if there * username deny for given rule set.
func (result *EnumerationResult) WildcardDenied() bool {
	return result.wildcardDenied
}

// NewEnumerationResult returns new EnumerationResult.
func NewEnumerationResult() EnumerationResult {
	return EnumerationResult{
		allowedDeniedMap: map[string]bool{},
		wildcardAllowed:  false,
		wildcardDenied:   false,
	}
}

// EnumerateDatabaseUsers works on a given role set to return a minimal description of allowed set of usernames.
// It is biased towards *allowed* usernames; It is meant to describe what the user can do, rather than cannot do.
// For that reason if the user isn't allowed to pick *any* entities, the output will be empty.
//
// In cases where * is listed in set of allowed users, it may be hard for users to figure out the expected username.
// For this reason the parameter extraUsers provides an extra set of users to be checked against RoleSet.
// This extra set of users may be sourced e.g. from user connection history.
func (set RoleSet) EnumerateDatabaseUsers(database types.Database, extraUsers ...string) EnumerationResult {
	result := NewEnumerationResult()

	// gather users for checking from the roles, check wildcards.
	var users []string
	for _, role := range set {
		wildcardAllowed := false
		wildcardDenied := false

		for _, user := range role.GetDatabaseUsers(types.Allow) {
			if user == types.Wildcard {
				wildcardAllowed = true
			} else {
				users = append(users, user)
			}
		}

		for _, user := range role.GetDatabaseUsers(types.Deny) {
			if user == types.Wildcard {
				wildcardDenied = true
			} else {
				users = append(users, user)
			}
		}

		result.wildcardDenied = result.wildcardDenied || wildcardDenied

		if err := NewRoleSet(role).checkAccess(database, AccessMFAParams{Verified: true}); err == nil {
			result.wildcardAllowed = result.wildcardAllowed || wildcardAllowed
		}

	}

	users = apiutils.Deduplicate(append(users, extraUsers...))

	// check each individual user against the database.
	for _, user := range users {
		err := set.checkAccess(database, AccessMFAParams{Verified: true}, &DatabaseUserMatcher{User: user})
		result.allowedDeniedMap[user] = err == nil
	}

	return result
}

// EnumerateServerLogins works on a given role set to return a minimal description of allowed set of logins.
// The wildcard selector is ignored, since it is now allowed for server logins
func (set RoleSet) EnumerateServerLogins(server types.Server) EnumerationResult {
	result := NewEnumerationResult()

	// gather logins for checking from the roles
	// no need to check for wildcards
	var logins []string
	for _, role := range set {
		logins = append(logins, role.GetLogins(types.Allow)...)
		logins = append(logins, role.GetLogins(types.Deny)...)
	}

	logins = apiutils.Deduplicate(logins)

	// check each individual user against the server.
	for _, user := range logins {
		err := set.checkAccess(server, AccessMFAParams{Verified: true}, NewLoginMatcher(user))
		result.allowedDeniedMap[user] = err == nil
	}

	return result
}

// MatchNamespace returns true if given list of namespace matches
// target namespace, wildcard matches everything.
func MatchNamespace(selectors []string, namespace string) (bool, string) {
	for _, n := range selectors {
		if n == namespace || n == types.Wildcard {
			return true, "matched"
		}
	}
	return false, fmt.Sprintf("no match, role selectors %v, server namespace: %v", selectors, namespace)
}

// MatchAWSRoleARN returns true if provided role ARN matches selectors.
func MatchAWSRoleARN(selectors []string, roleARN string) (bool, string) {
	for _, l := range selectors {
		if l == roleARN {
			return true, "matched"
		}
	}
	return false, fmt.Sprintf("no match, role selectors %v, role ARN: %v", selectors, roleARN)
}

// MatchDatabaseName returns true if provided database name matches selectors.
func MatchDatabaseName(selectors []string, name string) (bool, string) {
	for _, n := range selectors {
		if n == name || n == types.Wildcard {
			return true, "matched"
		}
	}
	return false, fmt.Sprintf("no match, role selectors %v, database name: %v", selectors, name)
}

// MatchDatabaseUser returns true if provided database user matches selectors.
func MatchDatabaseUser(selectors []string, user string) (bool, string) {
	for _, u := range selectors {
		if u == user || u == types.Wildcard {
			return true, "matched"
		}
	}
	return false, fmt.Sprintf("no match, role selectors %v, database user: %v", selectors, user)
}

// MatchLabels matches selector against target. Empty selector matches
// nothing, wildcard matches everything.
func MatchLabels(selector types.Labels, target map[string]string) (bool, string, error) {
	// Empty selector matches nothing.
	if len(selector) == 0 {
		return false, "no match, empty selector", nil
	}

	// *: * matches everything even empty target set.
	selectorValues := selector[types.Wildcard]
	if len(selectorValues) == 1 && selectorValues[0] == types.Wildcard {
		return true, "matched", nil
	}

	// Perform full match.
	for key, selectorValues := range selector {
		targetVal, hasKey := target[key]

		if !hasKey {
			return false, fmt.Sprintf("no key match: '%v'", key), nil
		}

		if !apiutils.SliceContainsStr(selectorValues, types.Wildcard) {
			result, err := utils.SliceMatchesRegex(targetVal, selectorValues)
			if err != nil {
				return false, "", trace.Wrap(err)
			} else if !result {
				return false, fmt.Sprintf("no value match: got '%v' want: '%v'", targetVal, selectorValues), nil
			}
		}
	}

	return true, "matched", nil
}

// RoleNames returns a slice with role names. Removes runtime roles like
// the default implicit role.
func (set RoleSet) RoleNames() []string {
	out := make([]string, 0, len(set))
	for _, r := range set {
		if r.GetName() == constants.DefaultImplicitRole {
			continue
		}
		out = append(out, r.GetName())
	}
	return out
}

// Roles returns the list underlying roles this RoleSet is based on.
func (set RoleSet) Roles() []types.Role {
	return append([]types.Role{}, set...)
}

// HasRole checks if the role set has the role
func (set RoleSet) HasRole(role string) bool {
	for _, r := range set {
		if r.GetName() == role {
			return true
		}
	}
	return false
}

// WithoutImplicit returns this role set with default implicit role filtered out.
func (set RoleSet) WithoutImplicit() (out RoleSet) {
	for _, r := range set {
		if r.GetName() == constants.DefaultImplicitRole {
			continue
		}
		out = append(out, r)
	}
	return out
}

// PinSourceIP determines if the role set should use source IP pinning.
// If one or more roles in the set requires IP pinning then it will be enabled.
func (set RoleSet) PinSourceIP() bool {
	for _, role := range set {
		if role.GetOptions().PinSourceIP {
			return true
		}
	}
	return false
}

// MFAParams returns MFA params for the given user given their roles, the cluster
// auth preference, and whether mfa has been verified.
func (set RoleSet) MFAParams(authPrefRequirement types.RequireMFAType) (params AccessMFAParams) {
	// per-session MFA is overridden by hardware key PIV touch requirement.
	// check if the auth pref or any roles have this option.
	if authPrefRequirement == types.RequireMFAType_HARDWARE_KEY_TOUCH {
		return AccessMFAParams{Required: MFARequiredNever}
	}
	for _, role := range set {
		if role.GetOptions().RequireMFAType == types.RequireMFAType_HARDWARE_KEY_TOUCH {
			return AccessMFAParams{Required: MFARequiredNever}
		}
	}

	// MFA is always required according to the cluster auth pref.
	if authPrefRequirement.IsSessionMFARequired() {
		return AccessMFAParams{Required: MFARequiredAlways}
	}

	// If MFA requirement is the same across all roles, we can skip the per-role check.
	// Set mfaRequired to the first role's requirement, then check if all other roles match.
	if len(set) > 0 {
		rolesMFARequired := set[0].GetOptions().RequireMFAType.IsSessionMFARequired()
		for _, role := range set[1:] {
			if role.GetOptions().RequireMFAType.IsSessionMFARequired() != rolesMFARequired {
				// This role differs from the MFA requirement of the other roles, return per-role.
				return AccessMFAParams{Required: MFARequiredPerRole}
			}
		}

		if rolesMFARequired {
			return AccessMFAParams{Required: MFARequiredAlways}
		}
	}

	// No roles to check or no roles require MFA.
	return AccessMFAParams{Required: MFARequiredNever}
}

// PrivateKeyPolicy returns the enforced private key policy for this role set.
func (set RoleSet) PrivateKeyPolicy(defaultPolicy keys.PrivateKeyPolicy) keys.PrivateKeyPolicy {
	if defaultPolicy == keys.PrivateKeyPolicyHardwareKeyTouch {
		// This is the strictest option so we can return now
		return defaultPolicy
	}

	policy := defaultPolicy
	for _, role := range set {
		switch rolePolicy := role.GetPrivateKeyPolicy(); rolePolicy {
		case keys.PrivateKeyPolicyHardwareKey:
			policy = rolePolicy
		case keys.PrivateKeyPolicyHardwareKeyTouch:
			// This is the strictest option so we can return now
			return keys.PrivateKeyPolicyHardwareKeyTouch
		}
	}

	return policy
}

// AdjustSessionTTL will reduce the requested ttl to the lowest max allowed TTL
// for this role set, otherwise it returns ttl unchanged
func (set RoleSet) AdjustSessionTTL(ttl time.Duration) time.Duration {
	for _, role := range set {
		maxSessionTTL := role.GetOptions().MaxSessionTTL.Value()
		if maxSessionTTL != 0 && ttl > maxSessionTTL {
			ttl = maxSessionTTL
		}
	}
	return ttl
}

// MaxConnections returns the maximum number of concurrent ssh connections
// allowed.  If MaxConnections is zero then no maximum was defined
// and the number of concurrent connections is unconstrained.
func (set RoleSet) MaxConnections() int64 {
	var mcs int64
	for _, role := range set {
		if m := role.GetOptions().MaxConnections; m != 0 && (m < mcs || mcs == 0) {
			mcs = m
		}
	}
	return mcs
}

// MaxSessions returns the maximum number of concurrent ssh sessions
// per connection.  If MaxSessions is zero then no maximum was defined
// and the number of sessions is unconstrained.
func (set RoleSet) MaxSessions() int64 {
	var ms int64
	for _, role := range set {
		if m := role.GetOptions().MaxSessions; m != 0 && (m < ms || ms == 0) {
			ms = m
		}
	}
	return ms
}

// MaxConnections returns the maximum number of concurrent Kubernetes connections
// allowed.  If MaxConnections is zero then no maximum was defined
// and the number of concurrent connections is unconstrained.
func (set RoleSet) MaxKubernetesConnections() int64 {
	var mcs int64
	for _, role := range set {
		if m := role.GetOptions().MaxKubernetesConnections; m != 0 && (m < mcs || mcs == 0) {
			mcs = m
		}
	}
	return mcs
}

// SessionPolicySets returns the list of SessionPolicySets for all roles.
func (set RoleSet) SessionPolicySets() []*types.SessionTrackerPolicySet {
	var policySets []*types.SessionTrackerPolicySet
	for _, role := range set {
		policySet := role.GetSessionPolicySet()
		policySets = append(policySets, &policySet)
	}
	return policySets
}

// AdjustClientIdleTimeout adjusts requested idle timeout
// to the lowest max allowed timeout, the most restrictive
// option will be picked, negative values will be assumed as 0
func (set RoleSet) AdjustClientIdleTimeout(timeout time.Duration) time.Duration {
	if timeout < 0 {
		timeout = 0
	}
	for _, role := range set {
		roleTimeout := role.GetOptions().ClientIdleTimeout
		// 0 means not set, so it can't be most restrictive, disregard it too
		if roleTimeout.Duration() <= 0 {
			continue
		}
		switch {
		// in case if timeout is 0, means that incoming value
		// does not restrict the idle timeout, pick any other value
		// set by the role
		case timeout == 0:
			timeout = roleTimeout.Duration()
		case roleTimeout.Duration() < timeout:
			timeout = roleTimeout.Duration()
		}
	}
	return timeout
}

// AdjustDisconnectExpiredCert adjusts the value based on the role set
// the most restrictive option will be picked
func (set RoleSet) AdjustDisconnectExpiredCert(disconnect bool) bool {
	for _, role := range set {
		if role.GetOptions().DisconnectExpiredCert.Value() {
			disconnect = true
		}
	}
	return disconnect
}

// CheckKubeGroupsAndUsers check if role can login into kubernetes
// and returns two lists of allowed groups and users
func (set RoleSet) CheckKubeGroupsAndUsers(ttl time.Duration, overrideTTL bool, matchers ...RoleMatcher) ([]string, []string, error) {
	groups := make(map[string]struct{})
	users := make(map[string]struct{})
	var matchedTTL bool
	for _, role := range set {
		ok, err := RoleMatchers(matchers).MatchAll(role, types.Allow)
		if err != nil {
			return nil, nil, trace.Wrap(err)
		}
		if !ok {
			continue
		}

		maxSessionTTL := role.GetOptions().MaxSessionTTL.Value()
		if overrideTTL || (ttl <= maxSessionTTL && maxSessionTTL != 0) {
			matchedTTL = true
			for _, group := range role.GetKubeGroups(types.Allow) {
				groups[group] = struct{}{}
			}
			for _, user := range role.GetKubeUsers(types.Allow) {
				users[user] = struct{}{}
			}
		}
	}
	for _, role := range set {
		ok, _, err := RoleMatchers(matchers).MatchAny(role, types.Deny)
		if err != nil {
			return nil, nil, trace.Wrap(err)
		}
		if !ok {
			continue
		}
		for _, group := range role.GetKubeGroups(types.Deny) {
			delete(groups, group)
		}
		for _, user := range role.GetKubeUsers(types.Deny) {
			delete(users, user)
		}
	}
	if !matchedTTL {
		return nil, nil, trace.AccessDenied("this user cannot request kubernetes access for %v", ttl)
	}
	if len(groups) == 0 && len(users) == 0 {
		return nil, nil, trace.NotFound("this user cannot request kubernetes access, has no assigned groups or users")
	}
	return utils.StringsSliceFromSet(groups), utils.StringsSliceFromSet(users), nil
}

// CheckDatabaseNamesAndUsers checks if the role has any allowed database
// names or users.
func (set RoleSet) CheckDatabaseNamesAndUsers(ttl time.Duration, overrideTTL bool) ([]string, []string, error) {
	names := make(map[string]struct{})
	users := make(map[string]struct{})
	var matchedTTL bool
	for _, role := range set {
		maxSessionTTL := role.GetOptions().MaxSessionTTL.Value()
		if overrideTTL || (ttl <= maxSessionTTL && maxSessionTTL != 0) {
			matchedTTL = true
			for _, name := range role.GetDatabaseNames(types.Allow) {
				names[name] = struct{}{}
			}
			for _, user := range role.GetDatabaseUsers(types.Allow) {
				users[user] = struct{}{}
			}
		}
	}
	for _, role := range set {
		for _, name := range role.GetDatabaseNames(types.Deny) {
			delete(names, name)
		}
		for _, user := range role.GetDatabaseUsers(types.Deny) {
			delete(users, user)
		}
	}
	if !matchedTTL {
		return nil, nil, trace.AccessDenied("this user cannot request database access for %v", ttl)
	}
	if len(names) == 0 && len(users) == 0 {
		return nil, nil, trace.NotFound("this user cannot request database access, has no assigned database names or users")
	}
	return utils.StringsSliceFromSet(names), utils.StringsSliceFromSet(users), nil
}

// CheckAWSRoleARNs returns a list of AWS role ARNs this role set is allowed to assume.
func (set RoleSet) CheckAWSRoleARNs(ttl time.Duration, overrideTTL bool) ([]string, error) {
	arns := make(map[string]struct{})
	var matchedTTL bool
	for _, role := range set {
		maxSessionTTL := role.GetOptions().MaxSessionTTL.Value()
		if overrideTTL || (ttl <= maxSessionTTL && maxSessionTTL != 0) {
			matchedTTL = true
			for _, arn := range role.GetAWSRoleARNs(types.Allow) {
				arns[arn] = struct{}{}
			}
		}
	}
	for _, role := range set {
		for _, arn := range role.GetAWSRoleARNs(types.Deny) {
			delete(arns, arn)
		}
	}
	if !matchedTTL {
		return nil, trace.AccessDenied("this user cannot request AWS management console access for %v", ttl)
	}
	if len(arns) == 0 {
		return nil, trace.NotFound("this user cannot request AWS management console, has no assigned role ARNs")
	}
	return utils.StringsSliceFromSet(arns), nil
}

// CheckLoginDuration checks if role set can login up to given duration and
// returns a combined list of allowed logins.
func (set RoleSet) CheckLoginDuration(ttl time.Duration) ([]string, error) {
	logins, matchedTTL := set.GetLoginsForTTL(ttl)
	if !matchedTTL {
		return nil, trace.AccessDenied("this user cannot request a certificate for %v", ttl)
	}

	if len(logins) == 0 && !set.hasPossibleLogins() {
		// user was deliberately configured to have no login capability,
		// but ssh certificates must contain at least one valid principal.
		// we add a single distinctive value which should be unique, and
		// will never be a valid unix login (due to leading '-').
		logins = []string{constants.NoLoginPrefix + uuid.New().String()}
	}

	if len(logins) == 0 {
		return nil, trace.AccessDenied("this user cannot create SSH sessions, has no allowed logins")
	}

	return logins, nil
}

// GetAllLogins returns all valid unix logins for the RoleSet.
func (set RoleSet) GetAllLogins() []string {
	logins, _ := set.GetLoginsForTTL(0)
	return logins
}

// GetLoginsForTTL collects all logins that are valid for the given TTL.  The matchedTTL
// value indicates whether the TTL is within scope of *any* role.  This helps to distinguish
// between TTLs which are categorically invalid, and TTLs which are theoretically valid
// but happen to grant no logins.
func (set RoleSet) GetLoginsForTTL(ttl time.Duration) (logins []string, matchedTTL bool) {
	for _, role := range set {
		maxSessionTTL := role.GetOptions().MaxSessionTTL.Value()
		if ttl <= maxSessionTTL && maxSessionTTL != 0 {
			matchedTTL = true
			logins = append(logins, role.GetLogins(types.Allow)...)
		}
	}
	return apiutils.Deduplicate(logins), matchedTTL
}

// CheckAccessToRemoteCluster checks if a role has access to remote cluster. Deny rules are
// checked first then allow rules. Access to a cluster is determined by
// namespaces, labels, and logins.
func (set RoleSet) CheckAccessToRemoteCluster(rc types.RemoteCluster) error {
	if len(set) == 0 {
		return trace.AccessDenied("access to cluster denied")
	}

	// Note: logging in this function only happens in debug mode, this is because
	// adding logging to this function (which is called on every server returned
	// by GetRemoteClusters) can slow down this function by 50x for large clusters!
	isDebugEnabled, debugf := rbacDebugLogger()

	rcLabels := rc.GetMetadata().Labels

	// For backwards compatibility, if there is no role in the set with labels and the cluster
	// has no labels, assume that the role set has access to the cluster.
	usesLabels := false
	for _, role := range set {
		if len(role.GetClusterLabels(types.Allow)) != 0 || len(role.GetClusterLabels(types.Deny)) != 0 {
			usesLabels = true
			break
		}
	}

	if !usesLabels && len(rcLabels) == 0 {
		debugf("Grant access to cluster %v - no role in %v uses cluster labels and the cluster is not labeled.",
			rc.GetName(), set.RoleNames())
		return nil
	}

	// Check deny rules first: a single matching label from
	// the deny role set prohibits access.
	var errs []error
	for _, role := range set {
		matchLabels, labelsMessage, err := MatchLabels(role.GetClusterLabels(types.Deny), rcLabels)
		if err != nil {
			return trace.Wrap(err)
		}
		if matchLabels {
			// This condition avoids formatting calls on large scale.
			debugf("Access to cluster %v denied, deny rule in %v matched; match(label=%v)",
				rc.GetName(), role.GetName(), labelsMessage)
			return trace.AccessDenied("access to cluster denied")
		}
	}

	// Check allow rules: label has to match in any role in the role set to be granted access.
	for _, role := range set {
		matchLabels, labelsMessage, err := MatchLabels(role.GetClusterLabels(types.Allow), rcLabels)
		debugf("Check access to role(%v) rc(%v, labels=%v) matchLabels=%v, msg=%v, err=%v allow=%v rcLabels=%v",
			role.GetName(), rc.GetName(), rcLabels, matchLabels, labelsMessage, err, role.GetClusterLabels(types.Allow), rcLabels)
		if err != nil {
			return trace.Wrap(err)
		}
		if matchLabels {
			return nil
		}
		if isDebugEnabled {
			deniedError := trace.AccessDenied("role=%v, match(label=%v)",
				role.GetName(), labelsMessage)
			errs = append(errs, deniedError)
		}
	}

	debugf("Access to cluster %v denied, no allow rule matched; %v", rc.GetName(), errs)
	return trace.AccessDenied("access to cluster denied")
}

func (set RoleSet) hasPossibleLogins() bool {
	for _, role := range set {
		if role.GetName() == constants.DefaultImplicitRole {
			continue
		}
		if len(role.GetLogins(types.Allow)) != 0 {
			return true
		}
	}
	return false
}

// AWSRoleARNMatcher matches a role against AWS role ARN.
type AWSRoleARNMatcher struct {
	RoleARN string
}

// Match matches database account name against provided role and condition.
func (m *AWSRoleARNMatcher) Match(role types.Role, condition types.RoleConditionType) (bool, error) {
	match, _ := MatchAWSRoleARN(role.GetAWSRoleARNs(condition), m.RoleARN)
	return match, nil
}

// String returns the matcher's string representation.
func (m *AWSRoleARNMatcher) String() string {
	return fmt.Sprintf("AWSRoleARNMatcher(RoleARN=%v)", m.RoleARN)
}

// CanImpersonateSomeone returns true if this checker has any impersonation rules
func (set RoleSet) CanImpersonateSomeone() bool {
	for _, role := range set {
		cond := role.GetImpersonateConditions(types.Allow)
		if !cond.IsEmpty() {
			return true
		}
	}
	return false
}

// CheckImpersonate returns nil if this role set can impersonate
// a user and their roles, returns AccessDenied otherwise
// CheckImpersonate checks whether current user is allowed to impersonate
// users and roles
func (set RoleSet) CheckImpersonate(currentUser, impersonateUser types.User, impersonateRoles []types.Role) error {
	ctx := &impersonateContext{
		user:            currentUser,
		impersonateUser: impersonateUser,
	}
	whereParser, err := newImpersonateWhereParser(ctx)
	if err != nil {
		return trace.Wrap(err)
	}
	// check deny: a single match on a deny rule prohibits access
	for _, role := range set {
		cond := role.GetImpersonateConditions(types.Deny)
		matched, err := matchDenyImpersonateCondition(cond, impersonateUser, impersonateRoles)
		if err != nil {
			return trace.Wrap(err)
		}
		if matched {
			return trace.AccessDenied("access denied to '%s' to impersonate user '%s' and roles '%s'", currentUser.GetName(), impersonateUser.GetName(), roleNames(impersonateRoles))
		}
	}

	// check allow: if matches, allow to impersonate
	for _, role := range set {
		cond := role.GetImpersonateConditions(types.Allow)
		matched, err := matchAllowImpersonateCondition(ctx, whereParser, cond, impersonateUser, impersonateRoles)
		if err != nil {
			return trace.Wrap(err)
		}
		if matched {
			return nil
		}
	}

	return trace.AccessDenied("access denied to '%s' to impersonate user '%s' and roles '%s'", currentUser.GetName(), impersonateUser.GetName(), roleNames(impersonateRoles))
}

// CheckImpersonateRoles validates that the current user can perform role-only impersonation
// of the given roles. Role-only impersonation requires an allow rule with
// roles but no users (and no user-less deny rules). All requested roles must
// be allowed for the check to succeed.
func (set RoleSet) CheckImpersonateRoles(currentUser types.User, impersonateRoles []types.Role) error {
	ctx := &impersonateContext{
		user: currentUser,
	}
	whereParser, err := newImpersonateWhereParser(ctx)
	if err != nil {
		return trace.Wrap(err)
	}

	// TODO: Unlike regular impersonation where all requested roles must be
	// granted by a single impersonation role, it would be reasonable to
	// request several roles whose `allow` conditions are split between
	// several roles. Our initial use-case doesn't require this, so for now
	// we'll assume all requested roles must be granted by a single `allow`.

	// check deny: a single match on a deny rule prohibits access
	for _, role := range set {
		cond := role.GetImpersonateConditions(types.Deny)
		matched, err := matchDenyRoleImpersonateCondition(cond, impersonateRoles)
		if err != nil {
			return trace.Wrap(err)
		}
		if matched {
			return trace.AccessDenied("access denied to '%s' to impersonate roles '%s'", currentUser.GetName(), roleNames(impersonateRoles))
		}
	}

	// check allow: if any one Role satisfies all the role requests, allow impersonation
	for _, role := range set {
		cond := role.GetImpersonateConditions(types.Allow)
		matched, err := matchAllowRoleImpersonateCondition(ctx, whereParser, cond, impersonateRoles)
		if err != nil {
			return trace.Wrap(err)
		}
		if matched {
			return nil
		}
	}

	return trace.AccessDenied("access denied to '%s' to impersonate roles '%s'", currentUser.GetName(), roleNames(impersonateRoles))
}

// LockingMode returns the locking mode to apply with this RoleSet.
func (set RoleSet) LockingMode(defaultMode constants.LockingMode) constants.LockingMode {
	mode := defaultMode
	for _, role := range set {
		options := role.GetOptions()
		if options.Lock == constants.LockingModeStrict {
			return constants.LockingModeStrict
		}
		if options.Lock != "" {
			mode = options.Lock
		}
	}
	return mode
}

// CertificateExtensions returns the list of extensions for each role in the RoleSet
func (set RoleSet) CertificateExtensions() []*types.CertExtension {
	var exts []*types.CertExtension
	for _, role := range set {
		exts = append(exts, role.GetOptions().CertExtensions...)
	}
	return exts
}

// SessionRecordingMode returns the recording mode for a specific service.
func (set RoleSet) SessionRecordingMode(service constants.SessionRecordingService) constants.SessionRecordingMode {
	defaultValue := constants.SessionRecordingModeBestEffort
	useDefault := true

	for _, role := range set {
		recordSession := role.GetOptions().RecordSession

		// If one of the default values is "strict", set it as the value.
		if recordSession.Default == constants.SessionRecordingModeStrict {
			defaultValue = constants.SessionRecordingModeStrict
		}

		var roleMode constants.SessionRecordingMode
		switch service {
		case constants.SessionRecordingServiceSSH:
			roleMode = recordSession.SSH
		}

		switch roleMode {
		case constants.SessionRecordingModeStrict:
			// Early return as "strict" since it is the strictest value.
			return constants.SessionRecordingModeStrict
		case constants.SessionRecordingModeBestEffort:
			useDefault = false
		}
	}

	// Return the strictest default value.
	if useDefault {
		return defaultValue
	}

	return constants.SessionRecordingModeBestEffort
}

func roleNames(roles []types.Role) string {
	out := make([]string, len(roles))
	for i := range roles {
		out[i] = roles[i].GetName()
	}
	return strings.Join(out, ", ")
}

// matchAllowImpersonateCondition matches impersonate condition,
// both user, role and where condition has to match
func matchAllowImpersonateCondition(ctx *impersonateContext, whereParser predicate.Parser, cond types.ImpersonateConditions, impersonateUser types.User, impersonateRoles []types.Role) (bool, error) {
	// User impersonation requires both users and roles. Roles with no users
	// must use RoleRequests instead; however, we can't treat this as an error
	// since this function is tested against all roles regardless of how
	// they'll be used.
	if len(cond.Users) == 0 || len(cond.Roles) == 0 {
		return false, nil
	}

	anyUser, err := parse.NewAnyMatcher(cond.Users)
	if err != nil {
		return false, trace.Wrap(err)
	}

	if !anyUser.Match(impersonateUser.GetName()) {
		return false, nil
	}

	anyRole, err := parse.NewAnyMatcher(cond.Roles)
	if err != nil {
		return false, trace.Wrap(err)
	}

	for _, impersonateRole := range impersonateRoles {
		if !anyRole.Match(impersonateRole.GetName()) {
			return false, nil
		}
		// TODO:
		// This set impersonateRole inside the ctx that is in turn used inside whereParser
		// which is created in CheckImpersonate above but is being used right below.
		// This is unfortunate interface of the parser, instead
		// parser should accept additional context as a first argument.
		ctx.impersonateRole = impersonateRole
		match, err := matchesImpersonateWhere(cond, whereParser)
		if err != nil {
			return false, trace.Wrap(err)
		}
		if !match {
			return false, nil
		}
	}

	return true, nil
}

// matchDenyImpersonateCondition matches impersonate condition,
// greedy is used for deny type rules, where any user or role can match
func matchDenyImpersonateCondition(cond types.ImpersonateConditions, impersonateUser types.User, impersonateRoles []types.Role) (bool, error) {
	// As above, user impersonation requires both users and roles. We can't
	// return an error to ensure role impersonation rules are allowed to exist
	// in the system.
	if len(cond.Users) == 0 || len(cond.Roles) == 0 {
		return false, nil
	}

	anyUser, err := parse.NewAnyMatcher(cond.Users)
	if err != nil {
		return false, trace.Wrap(err)
	}

	if anyUser.Match(impersonateUser.GetName()) {
		return true, nil
	}

	anyRole, err := parse.NewAnyMatcher(cond.Roles)
	if err != nil {
		return false, trace.Wrap(err)
	}

	for _, impersonateRole := range impersonateRoles {
		if anyRole.Match(impersonateRole.GetName()) {
			return true, nil
		}
	}

	return false, nil
}

// matchAllowRoleImpersonateCondition matches an allow impersonate condition
// specifically for role-only impersonation, where only roles are matched.
func matchAllowRoleImpersonateCondition(ctx *impersonateContext, whereParser predicate.Parser, cond types.ImpersonateConditions, impersonateRoles []types.Role) (bool, error) {
	// an empty set matches nothing
	if len(cond.Users) == 0 && len(cond.Roles) == 0 {
		return false, nil
	}

	// Role impersonation can never apply to users.
	if len(cond.Users) != 0 {
		return false, nil
	}

	// By this point, at least 1 role is guaranteed.
	anyRole, err := parse.NewAnyMatcher(cond.Roles)
	if err != nil {
		return false, trace.Wrap(err)
	}

	for _, impersonateRole := range impersonateRoles {
		if !anyRole.Match(impersonateRole.GetName()) {
			return false, nil
		}
		// TODO:
		// This set impersonateRole inside the ctx that is in turn used inside whereParser
		// which is created in CheckImpersonate above but is being used right below.
		// This is unfortunate interface of the parser, instead
		// parser should accept additional context as a first argument.
		ctx.impersonateRole = impersonateRole
		match, err := matchesImpersonateWhere(cond, whereParser)
		if err != nil {
			return false, trace.Wrap(err)
		}
		if !match {
			return false, nil
		}
	}

	return true, nil
}

// matchDenyRoleImpersonateCondition matches a deny impersonate condition
// specifically for role impersonation, where only roles are matched.
func matchDenyRoleImpersonateCondition(cond types.ImpersonateConditions, impersonateRoles []types.Role) (bool, error) {
	// an empty set matches nothing
	if len(cond.Users) == 0 && len(cond.Roles) == 0 {
		return false, nil
	}

	// Role impersonation can never apply to users.
	if len(cond.Users) != 0 {
		return false, nil
	}

	// By this point, at least 1 role is guaranteed.
	anyRole, err := parse.NewAnyMatcher(cond.Roles)
	if err != nil {
		return false, trace.Wrap(err)
	}

	for _, impersonateRole := range impersonateRoles {
		if anyRole.Match(impersonateRole.GetName()) {
			return true, nil
		}
	}

	return false, nil
}

// RoleMatcher defines an interface for a generic role matcher.
type RoleMatcher interface {
	Match(types.Role, types.RoleConditionType) (bool, error)
}

// RoleMatchers defines a list of matchers.
type RoleMatchers []RoleMatcher

// MatchAll returns true if all matchers in the set match.
func (m RoleMatchers) MatchAll(role types.Role, condition types.RoleConditionType) (bool, error) {
	for _, matcher := range m {
		match, err := matcher.Match(role, condition)
		if err != nil {
			return false, trace.Wrap(err)
		}
		if !match {
			return false, nil
		}
	}
	return true, nil
}

// MatchAny returns true if at least one of the matchers in the set matches.
//
// If the result is true, returns matcher that matched.
func (m RoleMatchers) MatchAny(role types.Role, condition types.RoleConditionType) (bool, RoleMatcher, error) {
	for _, matcher := range m {
		match, err := matcher.Match(role, condition)
		if err != nil {
			return false, nil, trace.Wrap(err)
		}
		if match {
			return true, matcher, nil
		}
	}
	return false, nil, nil
}

// DatabaseUserMatcher matches a role against database account name.
type DatabaseUserMatcher struct {
	User string
}

// Match matches database account name against provided role and condition.
func (m *DatabaseUserMatcher) Match(role types.Role, condition types.RoleConditionType) (bool, error) {
	match, _ := MatchDatabaseUser(role.GetDatabaseUsers(condition), m.User)
	return match, nil
}

// String returns the matcher's string representation.
func (m *DatabaseUserMatcher) String() string {
	return fmt.Sprintf("DatabaseUserMatcher(User=%v)", m.User)
}

// DatabaseNameMatcher matches a role against database name.
type DatabaseNameMatcher struct {
	Name string
}

// Match matches database name against provided role and condition.
func (m *DatabaseNameMatcher) Match(role types.Role, condition types.RoleConditionType) (bool, error) {
	match, _ := MatchDatabaseName(role.GetDatabaseNames(condition), m.Name)
	return match, nil
}

// String returns the matcher's string representation.
func (m *DatabaseNameMatcher) String() string {
	return fmt.Sprintf("DatabaseNameMatcher(Name=%v)", m.Name)
}

type loginMatcher struct {
	login string
}

// NewLoginMatcher creates a RoleMatcher that checks whether the role's logins
// match the specified condition.
func NewLoginMatcher(login string) RoleMatcher {
	return &loginMatcher{login: login}
}

// Match matches a login against a role.
func (l *loginMatcher) Match(role types.Role, typ types.RoleConditionType) (bool, error) {
	logins := role.GetLogins(typ)
	for _, login := range logins {
		if l.login == login {
			return true, nil
		}
	}
	return false, nil
}

type windowsLoginMatcher struct {
	login string
}

// NewWindowsLoginMatcher creates a RoleMatcher that checks whether the role's
// Windows desktop logins match the specified condition.
func NewWindowsLoginMatcher(login string) RoleMatcher {
	return &windowsLoginMatcher{login: login}
}

// Match matches a Windows Desktop login against a role.
func (l *windowsLoginMatcher) Match(role types.Role, typ types.RoleConditionType) (bool, error) {
	logins := role.GetWindowsLogins(typ)
	for _, login := range logins {
		if l.login == login {
			return true, nil
		}
	}
	return false, nil
}

type kubernetesClusterLabelMatcher struct {
	clusterLabels map[string]string
}

// NewKubernetesClusterLabelMatcher creates a RoleMatcher that checks whether a role's
// Kubernetes service labels match.
func NewKubernetesClusterLabelMatcher(clustersLabels map[string]string) RoleMatcher {
	return &kubernetesClusterLabelMatcher{clusterLabels: clustersLabels}
}

// Match matches a Kubernetes cluster labels against a role.
func (l *kubernetesClusterLabelMatcher) Match(role types.Role, typ types.RoleConditionType) (bool, error) {
	ok, _, err := MatchLabels(l.getKubeLabels(role, typ), l.clusterLabels)
	return ok, trace.Wrap(err)
}

// getKubeLabels returns kubernetes_labels based on resource version and role type.
func (l kubernetesClusterLabelMatcher) getKubeLabels(role types.Role, typ types.RoleConditionType) types.Labels {
	labels := role.GetKubernetesLabels(typ)

	// After the introduction of https://github.com/gravitational/teleport/pull/9759 the
	// kubernetes_labels started to be respected. Former role behavior evaluated deny rules
	// even if the kubernetes_labels was empty. To preserve this behavior after respecting kubernetes label the label
	// logic needs to be aligned.
	// Default wildcard rules should be added to  deny.kubernetes_labels if
	// deny.kubernetes_labels is empty to ensure that deny rule will be evaluated
	// even if kubernetes_labels are empty.
	if len(labels) == 0 && typ == types.Deny {
		return map[string]apiutils.Strings{types.Wildcard: []string{types.Wildcard}}
	}
	return labels
}

// AccessCheckable is the subset of types.Resource required for the RBAC checks.
type AccessCheckable interface {
	GetKind() string
	GetName() string
	GetMetadata() types.Metadata
	GetAllLabels() map[string]string
}

// rbacDebugLogger creates a debug logger for Teleport's RBAC component.
// It also returns a flag indicating whether debug logging is enabled,
// allowing the RBAC system to generate more verbose errors in debug mode.
func rbacDebugLogger() (debugEnabled bool, debugf func(format string, args ...interface{})) {
	isDebugEnabled := log.IsLevelEnabled(log.DebugLevel)
	log := log.WithField(trace.Component, teleport.ComponentRBAC)
	return isDebugEnabled, log.Debugf
}

// checkAccess checks if this role set has access to a particular resource,
// optionally matching the resource's labels.
func (set RoleSet) checkAccess(r AccessCheckable, mfa AccessMFAParams, matchers ...RoleMatcher) error {
	// Note: logging in this function only happens in debug mode. This is because
	// adding logging to this function (which is called on every resource returned
	// by the backend) can slow down this function by 50x for large clusters!
	isDebugEnabled, debugf := rbacDebugLogger()

	if mfa.Required == MFARequiredAlways && !mfa.Verified {
		debugf("Access to %v %q denied, cluster requires per-session MFA", r.GetKind(), r.GetName())
		return ErrSessionMFARequired
	}

	namespace := types.ProcessNamespace(r.GetMetadata().Namespace)
	allLabels := r.GetAllLabels()

	// Additional message depending on kind of resource
	// so there's more context on why the user might not have access.
	additionalDeniedMessage := ""

	var getRoleLabels func(types.Role, types.RoleConditionType) types.Labels
	switch r.GetKind() {
	case types.KindDatabase:
		getRoleLabels = types.Role.GetDatabaseLabels
		additionalDeniedMessage = "Confirm database user and name."
	case types.KindApp:
		getRoleLabels = types.Role.GetAppLabels
	case types.KindNode:
		getRoleLabels = types.Role.GetNodeLabels
		additionalDeniedMessage = "Confirm SSH login."
	case types.KindKubernetesCluster:
		getRoleLabels = types.Role.GetKubernetesLabels
		additionalDeniedMessage = "Confirm Kubernetes user or group."
	case types.KindWindowsDesktop:
		getRoleLabels = types.Role.GetWindowsDesktopLabels
		additionalDeniedMessage = "Confirm Windows user."
	case types.KindWindowsDesktopService:
		getRoleLabels = types.Role.GetWindowsDesktopLabels
	default:
		return trace.BadParameter("cannot match labels for kind %v", r.GetKind())
	}

	// Check deny rules.
	for _, role := range set {
		matchNamespace, namespaceMessage := MatchNamespace(role.GetNamespaces(types.Deny), namespace)
		if !matchNamespace {
			continue
		}

		matchLabels, labelsMessage, err := MatchLabels(getRoleLabels(role, types.Deny), allLabels)
		if err != nil {
			return trace.Wrap(err)
		}
		if matchLabels {
			debugf("Access to %v %q denied, deny rule in role %q matched; match(namespace=%v, label=%v)",
				r.GetKind(), r.GetName(), role.GetName(), namespaceMessage, labelsMessage)
			return trace.AccessDenied("access to %v denied. User does not have permissions. %v",
				r.GetKind(), additionalDeniedMessage)
		}

		// Deny rules are greedy on purpose. They will always match if
		// at least one of the matchers returns true.
		matchMatchers, matchersMessage, err := RoleMatchers(matchers).MatchAny(role, types.Deny)
		if err != nil {
			return trace.Wrap(err)
		}
		if matchMatchers {
			debugf("Access to %v %q denied, deny rule in role %q matched; match(matcher=%v)",
				r.GetKind(), r.GetName(), role.GetName(), matchersMessage)
			return trace.AccessDenied("access to %v denied. User does not have permissions. %v",
				r.GetKind(), additionalDeniedMessage)
		}
	}

	var errs []error
	allowed := false
	// Check allow rules.
	for _, role := range set {
		matchNamespace, namespaceMessage := MatchNamespace(role.GetNamespaces(types.Allow), namespace)
		if !matchNamespace {
			if isDebugEnabled {
				errs = append(errs, trace.AccessDenied("role=%v, match(namespace=%v)",
					role.GetName(), namespaceMessage))
			}
			continue
		}

		matchLabels, labelsMessage, err := MatchLabels(getRoleLabels(role, types.Allow), allLabels)
		if err != nil {
			return trace.Wrap(err)
		}
		if !matchLabels {
			if isDebugEnabled {
				errs = append(errs, trace.AccessDenied("role=%v, match(label=%v)",
					role.GetName(), labelsMessage))
			}
			continue
		}

		// Allow rules are not greedy. They will match only if all of the
		// matchers return true.
		matchMatchers, err := RoleMatchers(matchers).MatchAll(role, types.Allow)
		if err != nil {
			return trace.Wrap(err)
		}
		if !matchMatchers {
			if isDebugEnabled {
				errs = append(errs, fmt.Errorf("role=%v, match(matchers=%v)",
					role.GetName(), matchers))
			}
			continue
		}

		// if we've reached this point, namespace, labels, and matchers all match.
		// if MFA is verified or never required, we're done.
		if mfa.Verified || mfa.Required == MFARequiredNever {
			return nil
		}
		// if MFA is not verified and we require session MFA, deny access
		if role.GetOptions().RequireMFAType.IsSessionMFARequired() {
			debugf("Access to %v %q denied, role %q requires per-session MFA",
				r.GetKind(), r.GetName(), role.GetName())
			return ErrSessionMFARequired
		}

		// Check all remaining roles, even if we found a match.
		// RequireSessionMFA should be enforced when at least one role has
		// it.
		allowed = true
		debugf("Access to %v %q granted, allow rule in role %q matched.",
			r.GetKind(), r.GetName(), role.GetName())
	}

	if allowed {
		return nil
	}

	debugf("Access to %v %q denied, no allow rule matched; %v", r.GetKind(), r.GetName(), errs)
	return trace.AccessDenied("access to %v denied. User does not have permissions. %v",
		r.GetKind(), additionalDeniedMessage)
}

// CanForwardAgents returns true if role set allows forwarding agents.
func (set RoleSet) CanForwardAgents() bool {
	for _, role := range set {
		if role.GetOptions().ForwardAgent.Value() {
			return true
		}
	}
	return false
}

// CanPortForward returns true if a role in the RoleSet allows port forwarding.
func (set RoleSet) CanPortForward() bool {
	for _, role := range set {
		if types.BoolDefaultTrue(role.GetOptions().PortForwarding) {
			return true
		}
	}
	return false
}

// RecordDesktopSession returns true if the role set has enabled desktop
// session recording. Recording is considered enabled if at least one
// role in the set has enabled it.
func (set RoleSet) RecordDesktopSession() bool {
	for _, role := range set {
		var bo *types.BoolOption
		if role.GetOptions().RecordSession != nil {
			bo = role.GetOptions().RecordSession.Desktop
		}
		if types.BoolDefaultTrue(bo) {
			return true
		}
	}
	return false
}

// DesktopClipboard returns true if the role set has enabled shared
// clipboard for desktop sessions. Clipboard sharing is disabled if
// one or more of the roles in the set has disabled it.
func (set RoleSet) DesktopClipboard() bool {
	for _, role := range set {
		if !types.BoolDefaultTrue(role.GetOptions().DesktopClipboard) {
			return false
		}
	}
	return true
}

// DesktopDirectorySharing returns true if the role set has directory sharing
// enabled. This setting is disabled if one or more of the roles in the set has
// disabled it.
func (set RoleSet) DesktopDirectorySharing() bool {
	for _, role := range set {
		if !types.BoolDefaultTrue(role.GetOptions().DesktopDirectorySharing) {
			return false
		}
	}
	return true
}

// MaybeCanReviewRequests attempts to guess if this RoleSet belongs
// to a user who should be submitting access reviews.  Because not all rolesets
// are derived from statically assigned roles, this may return false positives.
func (set RoleSet) MaybeCanReviewRequests() bool {
	for _, role := range set {
		if !role.GetAccessReviewConditions(types.Allow).IsZero() {
			// at least one nonzero allow directive exists for
			// review submission.
			return true
		}
	}
	return false
}

// PermitX11Forwarding returns true if this RoleSet allows X11 Forwarding.
func (set RoleSet) PermitX11Forwarding() bool {
	for _, role := range set {
		if role.GetOptions().PermitX11Forwarding.Value() {
			return true
		}
	}
	return false
}

// CanCopyFiles returns true if the role set has enabled remote file
// operations via SCP or SFTP. Remote file operations are disabled if
// one or more of the roles in the set has disabled it.
func (set RoleSet) CanCopyFiles() bool {
	for _, role := range set {
		if !types.BoolDefaultTrue(role.GetOptions().SSHFileCopy) {
			return false
		}
	}
	return true
}

// CertificateFormat returns the most permissive certificate format in a
// RoleSet.
func (set RoleSet) CertificateFormat() string {
	var formats []string

	for _, role := range set {
		// get the certificate format for each individual role. if a role does not
		// have a certificate format (like implicit roles) skip over it
		certificateFormat := role.GetOptions().CertificateFormat
		if certificateFormat == "" {
			continue
		}

		formats = append(formats, certificateFormat)
	}

	// if no formats were found, return standard
	if len(formats) == 0 {
		return constants.CertificateFormatStandard
	}

	// sort the slice so the most permissive is the first element
	sort.Slice(formats, func(i, j int) bool {
		return certificatePriority(formats[i]) < certificatePriority(formats[j])
	})

	return formats[0]
}

// EnhancedRecordingSet returns the set of enhanced session recording
// events to capture for thi role set.
func (set RoleSet) EnhancedRecordingSet() map[string]bool {
	m := make(map[string]bool)

	// Loop over all roles and create a set of all options.
	for _, role := range set {
		for _, opt := range role.GetOptions().BPF {
			m[opt] = true
		}
	}

	return m
}

// HostUsers returns host user information matching a server or nil if
// a role disallows host user creation
func (set RoleSet) HostUsers(s types.Server) (*HostUsersInfo, error) {
	groups := make(map[string]struct{})
	sudoers := make(map[string]struct{})
	serverLabels := s.GetAllLabels()
	for _, role := range set {
		result, _, err := MatchLabels(role.GetNodeLabels(types.Allow), serverLabels)
		if err != nil {
			return nil, trace.Wrap(err)
		}
		// skip nodes that dont have matching labels
		if !result {
			continue
		}
		createHostUser := role.GetOptions().CreateHostUser
		// if any of the matching roles do not enable create host
		// user, the user should not be allowed on
		if createHostUser == nil || !createHostUser.Value {
			return nil, trace.AccessDenied("user is not allowed to create host users")
		}
		for _, group := range role.GetHostGroups(types.Allow) {
			groups[group] = struct{}{}
		}
		for _, sudoer := range role.GetHostSudoers(types.Allow) {
			sudoers[sudoer] = struct{}{}
		}
	}
	for _, role := range set {
		result, _, err := MatchLabels(role.GetNodeLabels(types.Deny), serverLabels)
		if err != nil {
			return nil, trace.Wrap(err)
		}
		if !result {
			continue
		}
		for _, group := range role.GetHostGroups(types.Deny) {
			delete(groups, group)
		}
		for _, sudoer := range role.GetHostSudoers(types.Deny) {
			if sudoer == "*" {
				sudoers = nil
				break
			}
			delete(sudoers, sudoer)
		}
	}

	return &HostUsersInfo{
		Groups:  utils.StringsSliceFromSet(groups),
		Sudoers: utils.StringsSliceFromSet(sudoers),
	}, nil
}

// certificatePriority returns the priority of the certificate format. The
// most permissive has lowest value.
func certificatePriority(s string) int {
	switch s {
	case teleport.CertificateFormatOldSSH:
		return 0
	case constants.CertificateFormatStandard:
		return 1
	default:
		return 2
	}
}

// CheckAgentForward checks if the role can request to forward the SSH agent
// for this user.
func (set RoleSet) CheckAgentForward(login string) error {
	// check if we have permission to login and forward agent. we don't check
	// for deny rules because if you can't forward an agent if you can't login
	// in the first place.
	for _, role := range set {
		for _, l := range role.GetLogins(types.Allow) {
			if role.GetOptions().ForwardAgent.Value() && l == login {
				return nil
			}
		}
	}
	return trace.AccessDenied("%v can not forward agent for %v", set, login)
}

func (set RoleSet) String() string {
	if len(set) == 0 {
		return "user without assigned roles"
	}
	roleNames := make([]string, len(set))
	for i, role := range set {
		roleNames[i] = role.GetName()
	}
	return fmt.Sprintf("roles %v", strings.Join(roleNames, ","))
}

// GuessIfAccessIsPossible guesses if access is possible for an entire category
// of resources.
// It responds the question: "is it possible that there is a resource of this
// kind that the current user can access?".
// GuessIfAccessIsPossible is used, mainly, for UI decisions ("should the tab
// for resource X appear"?). Most callers should use CheckAccessToRule instead.
func (set RoleSet) GuessIfAccessIsPossible(ctx RuleContext, namespace string, resource string, verb string, silent bool) error {
	// "Where" clause are handled differently by the method:
	// - "allow" rules have their "where" clause always match, as it's assumed
	//   that there could be a resource that matches it.
	// - "deny" rules have their "where" clause always fail, as it's assumed that
	//   there could be a resource that passes it.
	return set.checkAccessToRuleImpl(checkAccessParams{
		ctx:        ctx,
		namespace:  namespace,
		resource:   resource,
		verb:       verb,
		allowWhere: boolParser(true),  // always matches
		denyWhere:  boolParser(false), // never matches
		silent:     silent,
	})
}

type boolParser bool

func (p boolParser) Parse(string) (interface{}, error) {
	return predicate.BoolPredicate(func() bool {
		return bool(p)
	}), nil
}

// CheckAccessToRule checks if the RoleSet provides access in the given
// namespace to the specified resource and verb.
// silent controls whether the access violations are logged.
func (set RoleSet) CheckAccessToRule(ctx RuleContext, namespace string, resource string, verb string, silent bool) error {
	whereParser, err := NewWhereParser(ctx)
	if err != nil {
		return trace.Wrap(err)
	}

	return set.checkAccessToRuleImpl(checkAccessParams{
		ctx:        ctx,
		namespace:  namespace,
		resource:   resource,
		verb:       verb,
		allowWhere: whereParser,
		denyWhere:  whereParser,
		silent:     silent,
	})
}

type checkAccessParams struct {
	ctx                   RuleContext
	namespace             string
	resource              string
	verb                  string
	allowWhere, denyWhere predicate.Parser
	silent                bool
}

func (set RoleSet) checkAccessToRuleImpl(p checkAccessParams) error {
	actionsParser, err := NewActionsParser(p.ctx)
	if err != nil {
		return trace.Wrap(err)
	}

	// check deny: a single match on a deny rule prohibits access
	for _, role := range set {
		matchNamespace, _ := MatchNamespace(role.GetNamespaces(types.Deny), types.ProcessNamespace(p.namespace))
		if matchNamespace {
			matched, err := MakeRuleSet(role.GetRules(types.Deny)).Match(p.denyWhere, actionsParser, p.resource, p.verb)
			if err != nil {
				return trace.Wrap(err)
			}
			if matched {
				if !p.silent {
					log.WithFields(log.Fields{
						trace.Component: teleport.ComponentRBAC,
					}).Infof("Access to %v %v in namespace %v denied to %v: deny rule matched.",
						p.verb, p.resource, p.namespace, role.GetName())
				}
				return trace.AccessDenied("access denied to perform action %q on %q", p.verb, p.resource)
			}
		}
	}

	// check allow: if rule matches, grant access to resource
	for _, role := range set {
		matchNamespace, _ := MatchNamespace(role.GetNamespaces(types.Allow), types.ProcessNamespace(p.namespace))
		if matchNamespace {
			match, err := MakeRuleSet(role.GetRules(types.Allow)).Match(p.allowWhere, actionsParser, p.resource, p.verb)
			if err != nil {
				return trace.Wrap(err)
			}
			if match {
				return nil
			}
		}
	}

	if !p.silent {
		log.WithFields(log.Fields{
			trace.Component: teleport.ComponentRBAC,
		}).Infof("Access to %v %v in namespace %v denied to %v: no allow rule matched.",
			p.verb, p.resource, p.namespace, set)
	}
	return trace.AccessDenied("access denied to perform action %q on %q", p.verb, p.resource)
}

// ExtractConditionForIdentifier returns a restrictive filter expression
// for list queries based on the rules' `where` conditions.
func (set RoleSet) ExtractConditionForIdentifier(ctx RuleContext, namespace, resource, verb, identifier string) (*types.WhereExpr, error) {
	parser, err := newParserForIdentifierSubcondition(ctx, identifier)
	if err != nil {
		return nil, trace.Wrap(err)
	}
	parseWhere := func(rule types.Rule) (types.WhereExpr, error) {
		if rule.Where == "" {
			return types.WhereExpr{Literal: true}, nil
		}
		out, err := parser.Parse(rule.Where)
		if err != nil {
			return types.WhereExpr{}, trace.Wrap(err)
		}
		expr, ok := out.(types.WhereExpr)
		if !ok {
			return types.WhereExpr{}, trace.BadParameter("invalid type %T when extracting identifier subcondition from %q", out, rule.Where)
		}
		return expr, nil
	}

	// Gather identifier-related subconditions from the deny rules
	// and concatenate their negations by AND.
	var denyCond *types.WhereExpr
	for _, role := range set {
		matchNamespace, _ := MatchNamespace(role.GetNamespaces(types.Deny), types.ProcessNamespace(namespace))
		if !matchNamespace {
			continue
		}
		rules := MakeRuleSet(role.GetRules(types.Deny))
		for _, rule := range rules[resource] {
			if !rule.HasVerb(verb) && !rule.HasVerb(types.Wildcard) {
				continue
			}
			expr, err := parseWhere(rule)
			if err != nil {
				return nil, trace.Wrap(err)
			}
			if b, ok := expr.Literal.(bool); ok {
				if b {
					return nil, trace.AccessDenied("access denied to perform action %q on %q", verb, resource)
				}
				continue
			}
			negated := types.WhereExpr{Not: &expr}
			if denyCond == nil {
				denyCond = &negated
			} else {
				denyCond = &types.WhereExpr{And: types.WhereExpr2{L: denyCond, R: &negated}}
			}
		}
	}

	// Gather identifier-related subconditions from the allow rules
	// and concatenate by OR.
	var allowCond *types.WhereExpr
	for _, role := range set {
		matchNamespace, _ := MatchNamespace(role.GetNamespaces(types.Allow), types.ProcessNamespace(namespace))
		if !matchNamespace {
			continue
		}
		rules := MakeRuleSet(role.GetRules(types.Allow))
		for _, rule := range rules[resource] {
			if !rule.HasVerb(verb) && !rule.HasVerb(types.Wildcard) {
				continue
			}
			expr, err := parseWhere(rule)
			if err != nil {
				return nil, trace.Wrap(err)
			}
			if b, ok := expr.Literal.(bool); ok {
				if b {
					return denyCond, nil
				}
				continue
			}
			if allowCond == nil {
				allowCond = &expr
			} else {
				allowCond = &types.WhereExpr{Or: types.WhereExpr2{L: allowCond, R: &expr}}
			}
		}
	}

	if denyCond == nil {
		if allowCond == nil {
			return nil, trace.AccessDenied("access denied to perform action %q on %q", verb, resource)
		}
		return allowCond, nil
	}
	return &types.WhereExpr{And: types.WhereExpr2{L: denyCond, R: allowCond}}, nil
}

// GetSearchAsRoles returns all SearchAsRoles for this RoleSet.
func (set RoleSet) GetAllowedSearchAsRoles() []string {
	denied := make(map[string]struct{})
	var allowed []string
	for _, role := range set {
		for _, d := range role.GetSearchAsRoles(types.Deny) {
			denied[d] = struct{}{}
		}
	}
	for _, role := range set {
		for _, a := range role.GetSearchAsRoles(types.Allow) {
			if _, ok := denied[a]; !ok {
				allowed = append(allowed, a)
			}
		}
	}
	return apiutils.Deduplicate(allowed)
}

// GetAllowedPreviewAsRoles returns all PreviewAsRoles for this RoleSet.
func (set RoleSet) GetAllowedPreviewAsRoles() []string {
	denied := make(map[string]struct{})
	var allowed []string
	for _, role := range set {
		for _, d := range role.GetPreviewAsRoles(types.Deny) {
			denied[d] = struct{}{}
		}
	}
	for _, role := range set {
		for _, a := range role.GetPreviewAsRoles(types.Allow) {
			if _, ok := denied[a]; !ok {
				allowed = append(allowed, a)
			}
		}
	}
	return apiutils.Deduplicate(allowed)
}

// AccessMFAParams contains MFA-related parameters for methods that check access.
type AccessMFAParams struct {
	// Required determines whether a user's MFA requirement dynamically changes based on
	// their active role (per-role), or is static across all roles (always/never).
	Required MFARequired
	// Verified is set when MFA has been verified by the caller.
	Verified bool
}

// MFARequired determines when MFA is required for a user to access a resource.
type MFARequired string

const (
	// MFARequiredNever means that MFA is never required for any sessions started by this user. This either
	// means both the cluster auth preference and all roles have per-session MFA off, or at least one of
	// those resources has "require_session_mfa: hardware_key_touch", which overrides per-session MFA.
	MFARequiredNever MFARequired = "never"
	// MFARequiredAlways means that MFA is required for all sessions started by a user. This either
	// means that the cluster auth preference requires per-session MFA, or all of the user's roles require
	// per-session MFA
	MFARequiredAlways MFARequired = "always"
	// MFARequiredPerRole means that MFA requirement is based on which of the user's roles
	// provides access to the session in question.
	MFARequiredPerRole MFARequired = "per-role"
)

// SortedRoles sorts roles by name
type SortedRoles []types.Role

// Len returns length of a role list
func (s SortedRoles) Len() int {
	return len(s)
}

// Less compares roles by name
func (s SortedRoles) Less(i, j int) bool {
	return s[i].GetName() < s[j].GetName()
}

// Swap swaps two roles in a list
func (s SortedRoles) Swap(i, j int) {
	s[i], s[j] = s[j], s[i]
}

// UnmarshalRole unmarshals the Role resource from JSON.
func UnmarshalRole(bytes []byte, opts ...MarshalOption) (types.Role, error) {
	var h types.ResourceHeader
	err := json.Unmarshal(bytes, &h)
	if err != nil {
		return nil, trace.Wrap(err)
	}

	cfg, err := CollectOptions(opts)
	if err != nil {
		return nil, trace.Wrap(err)
	}

	switch h.Version {
	case types.V5:
		fallthrough
	case types.V4:
		// V4 roles are identical to V3 except for their defaults
		fallthrough
	case types.V3:
		var role types.RoleV5
		if err := utils.FastUnmarshal(bytes, &role); err != nil {
			return nil, trace.BadParameter(err.Error())
		}

		if err := ValidateRole(&role); err != nil {
			return nil, trace.Wrap(err)
		}

		if cfg.ID != 0 {
			role.SetResourceID(cfg.ID)
		}
		if !cfg.Expires.IsZero() {
			role.SetExpiry(cfg.Expires)
		}
		return &role, nil
	}

	return nil, trace.BadParameter("role version %q is not supported", h.Version)
}

// MarshalRole marshals the Role resource to JSON.
func MarshalRole(role types.Role, opts ...MarshalOption) ([]byte, error) {
	if err := ValidateRole(role); err != nil {
		return nil, trace.Wrap(err)
	}

	cfg, err := CollectOptions(opts)
	if err != nil {
		return nil, trace.Wrap(err)
	}

	switch role := role.(type) {
	case *types.RoleV5:
		if !cfg.PreserveResourceID {
			// avoid modifying the original object
			// to prevent unexpected data races
			copy := *role
			copy.SetResourceID(0)
			role = &copy
		}
		return utils.FastMarshal(role)
	default:
		return nil, trace.BadParameter("unrecognized role version %T", role)
	}
}

// DowngradeToV4 converts a V5 role to V4 so that it will be compatible with
// older instances. Makes a shallow copy if the conversion is necessary. The
// passed in role will not be mutated.
// DELETE IN 10.0.0
func DowngradeRoleToV4(r *types.RoleV5) (*types.RoleV5, error) {
	switch r.Version {
	case types.V3, types.V4:
		return r, nil
	case types.V5:
		var downgraded types.RoleV5
		downgraded = *r
		downgraded.Version = types.V4
		return &downgraded, nil
	default:
		return nil, trace.BadParameter("unrecognized role version %T", r.Version)
	}
}