init.go

/*
Copyright 2015 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 auth

import (
	"crypto/rsa"
	"crypto/tls"
	"crypto/x509"
	"crypto/x509/pkix"
	"fmt"
	"os"
	"path/filepath"
	"strings"
	"time"

	"github.com/gravitational/teleport"
	"github.com/gravitational/teleport/lib"
	"github.com/gravitational/teleport/lib/backend"
	"github.com/gravitational/teleport/lib/defaults"
	"github.com/gravitational/teleport/lib/events"
	"github.com/gravitational/teleport/lib/services"
	"github.com/gravitational/teleport/lib/sshca"
	"github.com/gravitational/teleport/lib/tlsca"
	"github.com/gravitational/teleport/lib/utils"

	"github.com/gravitational/trace"
	"github.com/pborman/uuid"
	"github.com/sirupsen/logrus"
	"golang.org/x/crypto/ssh"
)

var log = logrus.WithFields(logrus.Fields{
	trace.Component: teleport.ComponentAuth,
})

// InitConfig is auth server init config
type InitConfig struct {
	// Backend is auth backend to use
	Backend backend.Backend

	// Authority is key generator that we use
	Authority sshca.Authority

	// HostUUID is a UUID of this host
	HostUUID string

	// NodeName is the DNS name of the node
	NodeName string

	// ClusterName stores the FQDN of the signing CA (its certificate will have this
	// name embedded). It is usually set to the GUID of the host the Auth service runs on
	ClusterName services.ClusterName

	// Authorities is a list of pre-configured authorities to supply on first start
	Authorities []services.CertAuthority

	// AuthServiceName is a human-readable name of this CA. If several Auth services are running
	// (managing multiple teleport clusters) this field is used to tell them apart in UIs
	// It usually defaults to the hostname of the machine the Auth service runs on.
	AuthServiceName string

	// DataDir is the full path to the directory where keys, events and logs are kept
	DataDir string

	// ReverseTunnels is a list of reverse tunnels statically supplied
	// in configuration, so auth server will init the tunnels on the first start
	ReverseTunnels []services.ReverseTunnel

	// OIDCConnectors is a list of trusted OpenID Connect identity providers
	// in configuration, so auth server will init the tunnels on the first start
	OIDCConnectors []services.OIDCConnector

	// Trust is a service that manages users and credentials
	Trust services.Trust

	// Presence service is a discovery and hearbeat tracker
	Presence services.Presence

	// Provisioner is a service that keeps track of provisioning tokens
	Provisioner services.Provisioner

	// Identity is a service that manages users and credentials
	Identity services.Identity

	// Access is service controlling access to resources
	Access services.Access

	// ClusterConfiguration is a services that holds cluster wide configuration.
	ClusterConfiguration services.ClusterConfiguration

	// Roles is a set of roles to create
	Roles []services.Role

	// StaticTokens are pre-defined host provisioning tokens supplied via config file for
	// environments where paranoid security is not needed
	//StaticTokens []services.ProvisionToken
	StaticTokens services.StaticTokens

	// AuthPreference defines the authentication type (local, oidc) and second
	// factor (off, otp, u2f) passed in from a configuration file.
	AuthPreference services.AuthPreference

	// AuditLog is used for emitting events to audit log.
	AuditLog events.IAuditLog

	// ClusterConfig holds cluster level configuration.
	ClusterConfig services.ClusterConfig

	// SkipPeriodicOperations turns off periodic operations
	// used in tests that don't need periodc operations.
	SkipPeriodicOperations bool

	// KubeCACertPath is an optional path to kubernetes CA certificate authority
	KubeCACertPath string
}

// Init instantiates and configures an instance of AuthServer
func Init(cfg InitConfig, opts ...AuthServerOption) (*AuthServer, error) {
	if cfg.DataDir == "" {
		return nil, trace.BadParameter("DataDir: data dir can not be empty")
	}
	if cfg.HostUUID == "" {
		return nil, trace.BadParameter("HostUUID: host UUID can not be empty")
	}

	domainName := cfg.ClusterName.GetClusterName()
	err := cfg.Backend.AcquireLock(domainName, 30*time.Second)
	if err != nil {
		return nil, trace.Wrap(err)
	}
	defer cfg.Backend.ReleaseLock(domainName)

	// check that user CA and host CA are present and set the certs if needed
	asrv, err := NewAuthServer(&cfg, opts...)
	if err != nil {
		return nil, trace.Wrap(err)
	}

	// INTERNAL: Authorities (plus Roles) and ReverseTunnels don't follow the
	// same pattern as the rest of the configuration (they are not configuration
	// singletons). However, we need to keep them around while Telekube uses them.
	for _, role := range cfg.Roles {
		if err := asrv.UpsertRole(role, backend.Forever); err != nil {
			return nil, trace.Wrap(err)
		}
		log.Infof("Created role: %v.", role)
	}
	for i := range cfg.Authorities {
		ca := cfg.Authorities[i]
		ca, err = services.GetCertAuthorityMarshaler().GenerateCertAuthority(ca)
		if err != nil {
			return nil, trace.Wrap(err)
		}
		// Don't re-create CA if it already exists, otherwise
		// the existing cluster configuration will be corrupted;
		// this part of code is only used in tests.
		if err := asrv.Trust.CreateCertAuthority(ca); err != nil {
			if !trace.IsAlreadyExists(err) {
				return nil, trace.Wrap(err)
			}
		} else {
			log.Infof("Created trusted certificate authority: %q, type: %q.", ca.GetName(), ca.GetType())
		}
	}
	for _, tunnel := range cfg.ReverseTunnels {
		if err := asrv.UpsertReverseTunnel(tunnel); err != nil {
			return nil, trace.Wrap(err)
		}
		log.Infof("Created reverse tunnel: %v.", tunnel)
	}

	// set cluster level config on the backend and then force a sync of the cache.
	clusterConfig, err := asrv.GetClusterConfig()
	if err != nil && !trace.IsNotFound(err) {
		return nil, trace.Wrap(err)
	}
	// init a unique cluster ID, it must be set once only during the first
	// start so if it's already there, reuse it
	if clusterConfig != nil && clusterConfig.GetClusterID() != "" {
		cfg.ClusterConfig.SetClusterID(clusterConfig.GetClusterID())
	} else {
		cfg.ClusterConfig.SetClusterID(uuid.New())
	}
	err = asrv.SetClusterConfig(cfg.ClusterConfig)
	if err != nil {
		return nil, trace.Wrap(err)
	}

	// cluster name can only be set once. if it has already been set and we are
	// trying to update it to something else, hard fail.
	err = asrv.SetClusterName(cfg.ClusterName)
	if err != nil && !trace.IsAlreadyExists(err) {
		return nil, trace.Wrap(err)
	}
	if trace.IsAlreadyExists(err) {
		cn, err := asrv.GetClusterName()
		if err != nil {
			return nil, trace.Wrap(err)
		}
		if cn.GetClusterName() != cfg.ClusterName.GetClusterName() {
			return nil, trace.BadParameter("cannot rename cluster %q to %q: clusters cannot be renamed", cn.GetClusterName(), cfg.ClusterName.GetClusterName())
		}
	}
	log.Debugf("Cluster configuration: %v.", cfg.ClusterName)

	err = asrv.SetStaticTokens(cfg.StaticTokens)
	if err != nil {
		return nil, trace.Wrap(err)
	}
	log.Infof("Updating cluster configuration: %v.", cfg.StaticTokens)

	err = asrv.SetAuthPreference(cfg.AuthPreference)
	if err != nil {
		return nil, trace.Wrap(err)
	}
	log.Infof("Updating cluster configuration: %v.", cfg.AuthPreference)

	// always create the default namespace
	err = asrv.UpsertNamespace(services.NewNamespace(defaults.Namespace))
	if err != nil {
		return nil, trace.Wrap(err)
	}
	log.Infof("Created namespace: %q.", defaults.Namespace)

	// always create a default admin role
	defaultRole := services.NewAdminRole()
	err = asrv.CreateRole(defaultRole, backend.Forever)
	if err != nil && !trace.IsAlreadyExists(err) {
		return nil, trace.Wrap(err)
	}
	if !trace.IsAlreadyExists(err) {
		log.Infof("Created default admin role: %q.", defaultRole.GetName())
	}

	// generate a user certificate authority if it doesn't exist
	userCA, err := asrv.GetCertAuthority(services.CertAuthID{DomainName: cfg.ClusterName.GetClusterName(), Type: services.UserCA}, true)
	if err != nil {
		if !trace.IsNotFound(err) {
			return nil, trace.Wrap(err)
		}

		log.Infof("First start: generating user certificate authority.")
		priv, pub, err := asrv.GenerateKeyPair("")
		if err != nil {
			return nil, trace.Wrap(err)
		}

		keyPEM, certPEM, err := tlsca.GenerateSelfSignedCA(pkix.Name{
			CommonName:   cfg.ClusterName.GetClusterName(),
			Organization: []string{cfg.ClusterName.GetClusterName()},
		}, nil, defaults.CATTL)
		if err != nil {
			return nil, trace.Wrap(err)
		}

		userCA := &services.CertAuthorityV2{
			Kind:    services.KindCertAuthority,
			Version: services.V2,
			Metadata: services.Metadata{
				Name:      cfg.ClusterName.GetClusterName(),
				Namespace: defaults.Namespace,
			},
			Spec: services.CertAuthoritySpecV2{
				ClusterName:  cfg.ClusterName.GetClusterName(),
				Type:         services.UserCA,
				SigningKeys:  [][]byte{priv},
				CheckingKeys: [][]byte{pub},
				TLSKeyPairs:  []services.TLSKeyPair{{Cert: certPEM, Key: keyPEM}},
			},
		}

		if err := asrv.Trust.UpsertCertAuthority(userCA); err != nil {
			return nil, trace.Wrap(err)
		}
	} else if len(userCA.GetTLSKeyPairs()) == 0 {
		log.Infof("Migrate: generating TLS CA for existing user CA.")
		keyPEM, certPEM, err := tlsca.GenerateSelfSignedCA(pkix.Name{
			CommonName:   cfg.ClusterName.GetClusterName(),
			Organization: []string{cfg.ClusterName.GetClusterName()},
		}, nil, defaults.CATTL)
		if err != nil {
			return nil, trace.Wrap(err)
		}
		userCA.SetTLSKeyPairs([]services.TLSKeyPair{{Cert: certPEM, Key: keyPEM}})
		if err := asrv.Trust.UpsertCertAuthority(userCA); err != nil {
			return nil, trace.Wrap(err)
		}
	}

	// generate a host certificate authority if it doesn't exist
	hostCA, err := asrv.GetCertAuthority(services.CertAuthID{DomainName: cfg.ClusterName.GetClusterName(), Type: services.HostCA}, true)
	if err != nil {
		if !trace.IsNotFound(err) {
			return nil, trace.Wrap(err)
		}

		log.Infof("First start: generating host certificate authority.")
		priv, pub, err := asrv.GenerateKeyPair("")
		if err != nil {
			return nil, trace.Wrap(err)
		}

		keyPEM, certPEM, err := tlsca.GenerateSelfSignedCA(pkix.Name{
			CommonName:   cfg.ClusterName.GetClusterName(),
			Organization: []string{cfg.ClusterName.GetClusterName()},
		}, nil, defaults.CATTL)
		if err != nil {
			return nil, trace.Wrap(err)
		}
		hostCA = &services.CertAuthorityV2{
			Kind:    services.KindCertAuthority,
			Version: services.V2,
			Metadata: services.Metadata{
				Name:      cfg.ClusterName.GetClusterName(),
				Namespace: defaults.Namespace,
			},
			Spec: services.CertAuthoritySpecV2{
				ClusterName:  cfg.ClusterName.GetClusterName(),
				Type:         services.HostCA,
				SigningKeys:  [][]byte{priv},
				CheckingKeys: [][]byte{pub},
				TLSKeyPairs:  []services.TLSKeyPair{{Cert: certPEM, Key: keyPEM}},
			},
		}
		if err := asrv.Trust.UpsertCertAuthority(hostCA); err != nil {
			return nil, trace.Wrap(err)
		}
	} else if len(hostCA.GetTLSKeyPairs()) == 0 {
		log.Infof("Migrate: generating TLS CA for existing host CA.")
		privateKey, err := ssh.ParseRawPrivateKey(hostCA.GetSigningKeys()[0])
		if err != nil {
			return nil, trace.Wrap(err)
		}
		privateKeyRSA, ok := privateKey.(*rsa.PrivateKey)
		if !ok {
			return nil, trace.BadParameter("expected RSA private key, got %T", privateKey)
		}
		keyPEM, certPEM, err := tlsca.GenerateSelfSignedCAWithPrivateKey(privateKeyRSA, pkix.Name{
			CommonName:   cfg.ClusterName.GetClusterName(),
			Organization: []string{cfg.ClusterName.GetClusterName()},
		}, nil, defaults.CATTL)
		if err != nil {
			return nil, trace.Wrap(err)
		}
		hostCA.SetTLSKeyPairs([]services.TLSKeyPair{{Cert: certPEM, Key: keyPEM}})
		if err := asrv.Trust.UpsertCertAuthority(hostCA); err != nil {
			return nil, trace.Wrap(err)
		}
	}

	if lib.IsInsecureDevMode() {
		warningMessage := "Starting teleport in insecure mode. This is " +
			"dangerous! Sensitive information will be logged to console and " +
			"certificates will not be verified. Proceed with caution!"
		log.Warn(warningMessage)
	}

	// migrate any legacy resources to new format
	err = migrateLegacyResources(cfg, asrv)
	if err != nil {
		return nil, trace.Wrap(err)
	}

	return asrv, nil
}

func migrateLegacyResources(cfg InitConfig, asrv *AuthServer) error {
	err := migrateUsers(asrv)
	if err != nil {
		return trace.Wrap(err)
	}
	err = migrateRemoteClusters(asrv)
	if err != nil {
		return trace.Wrap(err)
	}
	err = migrateIdentities(cfg.DataDir)
	if err != nil {
		return trace.Wrap(err)
	}
	return nil
}

func migrateIdentities(dataDir string) error {
	storage, err := NewProcessStorage(filepath.Join(dataDir, teleport.ComponentProcess))
	if err != nil {
		return trace.Wrap(err)
	}
	for _, role := range []teleport.Role{teleport.RoleAdmin, teleport.RoleProxy, teleport.RoleNode} {
		if err := migrateIdentity(role, dataDir, storage); err != nil {
			return trace.Wrap(err)
		}
	}
	return nil
}

func migrateIdentity(role teleport.Role, dataDir string, storage *ProcessStorage) error {
	identity, err := readIdentityCompat(dataDir, IdentityID{Role: role})
	if err != nil {
		if !trace.IsNotFound(err) {
			return trace.Wrap(err)
		}
		return nil
	}
	err = storage.WriteIdentity(IdentityCurrent, *identity)
	if err != nil {
		return trace.Wrap(err)
	}
	err = removeIdentityCompat(dataDir, IdentityID{Role: role})
	if err != nil {
		if !trace.IsNotFound(err) {
			return trace.Wrap(err)
		}
	}
	log.Infof("Identity %v has been migrated to new on-disk format.", role)
	return nil
}

func migrateUsers(asrv *AuthServer) error {
	users, err := asrv.GetUsers()
	if err != nil {
		return trace.Wrap(err)
	}

	for i := range users {
		user := users[i]
		raw, ok := (user.GetRawObject()).(services.UserV1)
		if !ok {
			continue
		}
		log.Infof("Migrating legacy user: %v.", user.GetName())

		// create role for user and upsert to backend
		role := services.RoleForUser(user)
		role.SetLogins(services.Allow, raw.AllowedLogins)
		err = asrv.UpsertRole(role, backend.Forever)
		if err != nil {
			return trace.Wrap(err)
		}

		// upsert new user to backend
		user.AddRole(role.GetName())
		if err := asrv.UpsertUser(user); err != nil {
			return trace.Wrap(err)
		}
	}

	return nil
}

// isFirstStart returns 'true' if the auth server is starting for the 1st time
// on this server.
func isFirstStart(authServer *AuthServer, cfg InitConfig) (bool, error) {
	// check if the CA exists?
	_, err := authServer.GetCertAuthority(
		services.CertAuthID{
			DomainName: cfg.ClusterName.GetClusterName(),
			Type:       services.HostCA,
		}, false)
	if err != nil {
		if !trace.IsNotFound(err) {
			return false, trace.Wrap(err)
		}
		// CA not found? --> first start!
		return true, nil
	}
	return false, nil
}

// GenerateIdentity generates identity for the auth server
func GenerateIdentity(a *AuthServer, id IdentityID, additionalPrincipals []string) (*Identity, error) {
	keys, err := a.GenerateServerKeys(GenerateServerKeysRequest{
		HostID:               id.HostUUID,
		NodeName:             id.NodeName,
		Roles:                teleport.Roles{id.Role},
		AdditionalPrincipals: additionalPrincipals,
	})
	if err != nil {
		return nil, trace.Wrap(err)
	}
	return ReadIdentityFromKeyPair(keys.Key, keys.Cert, keys.TLSCert, keys.TLSCACerts)
}

// Identity is collection of certificates and signers that represent server identity
type Identity struct {
	// ID specifies server unique ID, name and role
	ID IdentityID
	// KeyBytes is a PEM encoded private key
	KeyBytes []byte
	// CertBytes is a PEM encoded SSH host cert
	CertBytes []byte
	// TLSCertBytes is a PEM encoded TLS x509 client certificate
	TLSCertBytes []byte
	// TLSCACertBytes is a list of PEM encoded TLS x509 certificate of certificate authority
	// associated with auth server services
	TLSCACertsBytes [][]byte
	// KeySigner is an SSH host certificate signer
	KeySigner ssh.Signer
	// Cert is a parsed SSH certificate
	Cert *ssh.Certificate
	// ClusterName is a name of host's cluster
	ClusterName string
}

// String returns user-friendly representation of the identity.
func (i *Identity) String() string {
	var out []string
	cert, err := tlsca.ParseCertificatePEM(i.TLSCertBytes)
	if err != nil {
		out = append(out, err.Error())
	} else {
		out = append(out, fmt.Sprintf("cert(%v issued by %v:%v)", cert.Subject.CommonName, cert.Issuer.CommonName, cert.Issuer.SerialNumber))
	}
	for j := range i.TLSCACertsBytes {
		cert, err := tlsca.ParseCertificatePEM(i.TLSCACertsBytes[j])
		if err != nil {
			out = append(out, err.Error())
		} else {
			out = append(out, fmt.Sprintf("trust root(%v:%v)", cert.Subject.CommonName, cert.Subject.SerialNumber))
		}
	}
	return fmt.Sprintf("Identity(%v, %v)", i.ID.Role, strings.Join(out, ","))
}

// HasTSLConfig returns true if this identity has TLS certificate and private key
func (i *Identity) HasTLSConfig() bool {
	return len(i.TLSCACertsBytes) != 0 && len(i.TLSCertBytes) != 0
}

// HasPrincipals returns whether identity has principals
func (i *Identity) HasPrincipals(additionalPrincipals []string) bool {
	set := utils.StringsSet(i.Cert.ValidPrincipals)
	for _, principal := range additionalPrincipals {
		if _, ok := set[principal]; !ok {
			return false
		}
	}
	return true
}

// TLSConfig returns TLS config for mutual TLS authentication
// can return NotFound error if there are no TLS credentials setup for identity
func (i *Identity) TLSConfig() (*tls.Config, error) {
	tlsConfig := utils.TLSConfig()
	if !i.HasTLSConfig() {
		return nil, trace.NotFound("no TLS credentials setup for this identity")
	}
	tlsCert, err := tls.X509KeyPair(i.TLSCertBytes, i.KeyBytes)
	if err != nil {
		return nil, trace.BadParameter("failed to parse private key: %v", err)
	}
	certPool := x509.NewCertPool()
	for j := range i.TLSCACertsBytes {
		parsedCert, err := tlsca.ParseCertificatePEM(i.TLSCACertsBytes[j])
		if err != nil {
			return nil, trace.Wrap(err, "failed to parse CA certificate")
		}
		certPool.AddCert(parsedCert)
	}
	tlsConfig.Certificates = []tls.Certificate{tlsCert}
	tlsConfig.RootCAs = certPool
	tlsConfig.ClientCAs = certPool
	return tlsConfig, nil
}

// IdentityID is a combination of role, host UUID, and node name.
type IdentityID struct {
	Role     teleport.Role
	HostUUID string
	NodeName string
}

// HostID is host ID part of the host UUID that consists cluster name
func (id *IdentityID) HostID() (string, error) {
	parts := strings.Split(id.HostUUID, ".")
	if len(parts) < 2 {
		return "", trace.BadParameter("expected 2 parts in %q", id.HostUUID)
	}
	return parts[0], nil
}

// Equals returns true if two identities are equal
func (id *IdentityID) Equals(other IdentityID) bool {
	return id.Role == other.Role && id.HostUUID == other.HostUUID
}

// String returns debug friendly representation of this identity
func (id *IdentityID) String() string {
	return fmt.Sprintf("Identity(hostuuid=%v, role=%v)", id.HostUUID, id.Role)
}

// ReadIdentityFromKeyPair reads TLS identity from key pair
func ReadIdentityFromKeyPair(keyBytes, sshCertBytes, tlsCertBytes []byte, tlsCACertsBytes [][]byte) (*Identity, error) {
	identity, err := ReadSSHIdentityFromKeyPair(keyBytes, sshCertBytes)
	if err != nil {
		return nil, trace.Wrap(err)
	}
	if len(tlsCertBytes) != 0 {
		// just to verify that identity parses properly for future use
		_, err := ReadTLSIdentityFromKeyPair(keyBytes, tlsCertBytes, tlsCACertsBytes)
		if err != nil {
			return nil, trace.Wrap(err)
		}
		identity.TLSCertBytes = tlsCertBytes
		identity.TLSCACertsBytes = tlsCACertsBytes
	}
	return identity, nil
}

// ReadTLSIdentityFromKeyPair reads TLS identity from key pair
func ReadTLSIdentityFromKeyPair(keyBytes, certBytes []byte, caCertsBytes [][]byte) (*Identity, error) {
	if len(keyBytes) == 0 {
		return nil, trace.BadParameter("missing private key")
	}

	if len(certBytes) == 0 {
		return nil, trace.BadParameter("missing certificate")
	}

	cert, err := tlsca.ParseCertificatePEM(certBytes)
	if err != nil {
		return nil, trace.Wrap(err, "failed to parse TLS certificate")
	}

	id, err := tlsca.FromSubject(cert.Subject)
	if err != nil {
		return nil, trace.Wrap(err)
	}

	if len(cert.Issuer.Organization) == 0 {
		return nil, trace.BadParameter("missing CA organization")
	}

	clusterName := cert.Issuer.Organization[0]
	if clusterName == "" {
		return nil, trace.BadParameter("misssing cluster name")
	}
	identity := &Identity{
		ID:              IdentityID{HostUUID: id.Username, Role: teleport.Role(id.Groups[0])},
		ClusterName:     clusterName,
		KeyBytes:        keyBytes,
		TLSCertBytes:    certBytes,
		TLSCACertsBytes: caCertsBytes,
	}
	_, err = identity.TLSConfig()
	if err != nil {
		return nil, trace.Wrap(err)
	}
	return identity, nil
}

// ReadSSHIdentityFromKeyPair reads identity from initialized keypair
func ReadSSHIdentityFromKeyPair(keyBytes, certBytes []byte) (*Identity, error) {
	if len(keyBytes) == 0 {
		return nil, trace.BadParameter("PrivateKey: missing private key")
	}

	if len(certBytes) == 0 {
		return nil, trace.BadParameter("Cert: missing parameter")
	}

	pubKey, _, _, _, err := ssh.ParseAuthorizedKey(certBytes)
	if err != nil {
		return nil, trace.BadParameter("failed to parse server certificate: %v", err)
	}

	cert, ok := pubKey.(*ssh.Certificate)
	if !ok {
		return nil, trace.BadParameter("expected ssh.Certificate, got %v", pubKey)
	}

	signer, err := ssh.ParsePrivateKey(keyBytes)
	if err != nil {
		return nil, trace.BadParameter("failed to parse private key: %v", err)
	}
	// this signer authenticates using certificate signed by the cert authority
	// not only by the public key
	certSigner, err := ssh.NewCertSigner(cert, signer)
	if err != nil {
		return nil, trace.BadParameter("unsupported private key: %v", err)
	}

	// check principals on certificate
	if len(cert.ValidPrincipals) < 1 {
		return nil, trace.BadParameter("valid principals: at least one valid principal is required")
	}
	for _, validPrincipal := range cert.ValidPrincipals {
		if validPrincipal == "" {
			return nil, trace.BadParameter("valid principal can not be empty: %q", cert.ValidPrincipals)
		}
	}

	// check permissions on certificate
	if len(cert.Permissions.Extensions) == 0 {
		return nil, trace.BadParameter("extensions: misssing needed extensions for host roles")
	}
	roleString := cert.Permissions.Extensions[utils.CertExtensionRole]
	if roleString == "" {
		return nil, trace.BadParameter("misssing cert extension %v", utils.CertExtensionRole)
	}
	roles, err := teleport.ParseRoles(roleString)
	if err != nil {
		return nil, trace.Wrap(err)
	}
	foundRoles := len(roles)
	if foundRoles != 1 {
		return nil, trace.Errorf("expected one role per certificate. found %d: '%s'",
			foundRoles, roles.String())
	}
	role := roles[0]
	clusterName := cert.Permissions.Extensions[utils.CertExtensionAuthority]
	if clusterName == "" {
		return nil, trace.BadParameter("missing cert extension %v", utils.CertExtensionAuthority)
	}

	return &Identity{
		ID:          IdentityID{HostUUID: cert.ValidPrincipals[0], Role: role},
		ClusterName: clusterName,
		KeyBytes:    keyBytes,
		CertBytes:   certBytes,
		KeySigner:   certSigner,
		Cert:        cert,
	}, nil
}

// ReadLocalIdentity reads, parses and returns the given pub/pri key + cert from the
// key storage (dataDir).
func ReadLocalIdentity(dataDir string, id IdentityID) (*Identity, error) {
	storage, err := NewProcessStorage(dataDir)
	if err != nil {
		return nil, trace.Wrap(err)
	}
	defer storage.Close()
	return storage.ReadIdentity(IdentityCurrent, id.Role)
}

// DELETE IN(2.7.0)
// removeIdentityCompat removes identity from disk
func removeIdentityCompat(dataDir string, id IdentityID) error {
	path := keysPath(dataDir, id)
	for _, filePath := range []string{path.key, path.sshCert, path.tlsCert, path.tlsCACert} {
		err := trace.ConvertSystemError(os.Remove(filePath))
		if err != nil {
			if !trace.IsNotFound(err) {
				return trace.Wrap(err)
			}
		}
	}
	return nil
}

// DELETE IN: 2.7.0
// NOTE: Sadly, our integration tests depend on this logic
// because they create remote cluster resource. Our integration
// tests should be migrated to use trusted clusters instead of manually
// creating tunnels.
// This migration adds remote cluster resource migrating from 2.5.0
// where the presence of remote cluster was identified only by presence
// of host certificate authority with cluster name not equal local cluster name
func migrateRemoteClusters(asrv *AuthServer) error {
	clusterName, err := asrv.GetClusterName()
	if err != nil {
		return trace.Wrap(err)
	}
	certAuthorities, err := asrv.GetCertAuthorities(services.HostCA, false)
	if err != nil {
		return trace.Wrap(err)
	}
	// loop over all roles and make sure any v3 roles have permit port
	// forward and forward agent allowed
	for _, certAuthority := range certAuthorities {
		if certAuthority.GetName() == clusterName.GetClusterName() {
			log.Debugf("Migrations: skipping local cluster cert authority %q.", certAuthority.GetName())
			continue
		}
		// remote cluster already exists
		_, err = asrv.GetRemoteCluster(certAuthority.GetName())
		if err == nil {
			log.Debugf("Migrations: remote cluster already exists for cert authority %q.", certAuthority.GetName())
			continue
		}
		if !trace.IsNotFound(err) {
			return trace.Wrap(err)
		}
		// the cert authority is associated with trusted cluster
		_, err = asrv.GetTrustedCluster(certAuthority.GetName())
		if err == nil {
			log.Debugf("Migrations: trusted cluster resource exists for cert authority %q.", certAuthority.GetName())
			continue
		}
		if !trace.IsNotFound(err) {
			return trace.Wrap(err)
		}
		remoteCluster, err := services.NewRemoteCluster(certAuthority.GetName())
		if err != nil {
			return trace.Wrap(err)
		}
		err = asrv.CreateRemoteCluster(remoteCluster)
		if err != nil {
			if !trace.IsAlreadyExists(err) {
				return trace.Wrap(err)
			}
		}
		log.Infof("Migrations: added remote cluster resource for cert authority %q.", certAuthority.GetName())
	}

	return nil
}

// DELETE IN(2.7.0)
// readIdentityCompat reads, parses and returns the given pub/pri key + cert from the
// key storage (dataDir). Used for data migrations
func readIdentityCompat(dataDir string, id IdentityID) (i *Identity, err error) {
	path := keysPath(dataDir, id)

	keyBytes, err := utils.ReadPath(path.key)
	if err != nil {
		return nil, trace.Wrap(err)
	}

	sshCertBytes, err := utils.ReadPath(path.sshCert)
	if err != nil {
		return nil, trace.Wrap(err)
	}

	// initially ignore absence of TLS identity for read purposes
	tlsCertBytes, err := utils.ReadPath(path.tlsCert)
	if err != nil {
		if !trace.IsNotFound(err) {
			return nil, trace.Wrap(err)
		}
	}

	tlsCACertBytes, err := utils.ReadPath(path.tlsCACert)
	if err != nil {
		if !trace.IsNotFound(err) {
			return nil, trace.Wrap(err)
		}
	}

	identity, err := ReadIdentityFromKeyPair(keyBytes, sshCertBytes, tlsCertBytes, [][]byte{tlsCACertBytes})
	if err != nil {
		return nil, trace.Wrap(err)
	}

	// Inject nodename back into identity read from disk.
	identity.ID.NodeName = id.NodeName

	return identity, nil
}

// DELETE IN(2.7.0)
type paths struct {
	dataDir   string
	key       string
	sshCert   string
	tlsCert   string
	tlsCACert string
}

// DELETE IN(2.7.0)
// keysPath returns two full file paths: to the host.key and host.cert
func keysPath(dataDir string, id IdentityID) paths {
	return paths{
		key:       filepath.Join(dataDir, fmt.Sprintf("%s.key", strings.ToLower(string(id.Role)))),
		sshCert:   filepath.Join(dataDir, fmt.Sprintf("%s.cert", strings.ToLower(string(id.Role)))),
		tlsCert:   filepath.Join(dataDir, fmt.Sprintf("%s.tlscert", strings.ToLower(string(id.Role)))),
		tlsCACert: filepath.Join(dataDir, fmt.Sprintf("%s.tlscacert", strings.ToLower(string(id.Role)))),
	}
}