creds.go

package tcclient

import (
	"context"
	"crypto/hmac"
	"crypto/sha256"
	"encoding/base64"
	"encoding/json"
	"errors"
	"fmt"
	"os"
	"strconv"
	"strings"
	"time"

	"github.com/taskcluster/httpbackoff/v3"
	"github.com/taskcluster/slugid-go/slugid"
	"github.com/taskcluster/taskcluster/v49/tools/jsonschema2go/text"
)

// Credentials represents the set of credentials required to access protected
// Taskcluster HTTP APIs.
type Credentials struct {
	// ClientID
	ClientID string `json:"clientId"`
	// AccessToken
	AccessToken string `json:"accessToken"`
	// Certificate used only for temporary credentials
	Certificate string `json:"certificate"`
	// AuthorizedScopes if set to nil, is ignored. Otherwise, it should be a
	// subset of the scopes that the ClientId already has, and restricts the
	// Credentials to only having these scopes. This is useful when performing
	// actions on behalf of a client which has more restricted scopes. Setting
	// to nil is not the same as setting to an empty array. If AuthorizedScopes
	// is set to an empty array rather than nil, this is equivalent to having
	// no scopes at all.
	// See https://docs.taskcluster.net/docs/manual/design/apis/hawk/authorized-scopes
	AuthorizedScopes []string `json:"authorizedScopes"`
}

func (creds *Credentials) String() string {
	return fmt.Sprintf(
		"ClientId: %q\nAccessToken: %q\nCertificate: %q\nAuthorizedScopes: %q",
		creds.ClientID,
		text.StarOut(creds.AccessToken),
		creds.Certificate,
		creds.AuthorizedScopes,
	)
}

// Client is the entry point into all the functionality in this package. It
// contains authentication credentials, and a service endpoint, which are
// required for all HTTP operations.
type Client struct {
	Credentials *Credentials
	// The Root URL of the Taskcluster deployment
	RootURL string
	// The (short) name of the service being accessed
	ServiceName string
	// The API version of the service being accessed
	APIVersion string
	// Whether authentication is enabled (e.g. set to 'false' when using taskcluster-proxy)
	Authenticate bool
	// HTTPClient is a ReducedHTTPClient to be used for the http call instead of
	// the DefaultHTTPClient.
	HTTPClient ReducedHTTPClient
	// Context that aborts all requests with this client
	Context context.Context
	// HTTPBackoffClient holds the HTTP backoff settings for retries
	HTTPBackoffClient *httpbackoff.Client
}

// Certificate represents the certificate used in Temporary Credentials. See
// https://docs.taskcluster.net/docs/manual/design/apis/hawk/temporary-credentials
type Certificate struct {
	Version   int      `json:"version"`
	Scopes    []string `json:"scopes"`
	Start     int64    `json:"start"`
	Expiry    int64    `json:"expiry"`
	Seed      string   `json:"seed"`
	Signature string   `json:"signature"`
	Issuer    string   `json:"issuer,omitempty"`
}

// CreateNamedTemporaryCredentials generates temporary credentials from permanent
// credentials, valid for the given duration, starting immediately.  The
// temporary credentials' scopes must be a subset of the permanent credentials'
// scopes. The duration may not be more than 31 days. Any authorized scopes of
// the permanent credentials will be passed through as authorized scopes to the
// temporary credentials, but will not be restricted via the certificate.
//
// Note that the auth service already applies a 5 minute clock skew to the
// start and expiry times in
// https://github.com/taskcluster/taskcluster-auth/pull/117 so no clock skew is
// applied in this method, nor should be applied by the caller.
//
// See https://docs.taskcluster.net/docs/manual/design/apis/hawk/temporary-credentials
func (permaCreds *Credentials) CreateNamedTemporaryCredentials(tempClientID string, duration time.Duration, scopes ...string) (tempCreds *Credentials, err error) {
	if duration > 31*24*time.Hour {
		return nil, errors.New("Temporary credentials must expire within 31 days; however a duration of " + duration.String() + " was specified to (*tcclient.Client).CreateTemporaryCredentials(...) method")
	}

	now := time.Now()
	start := now
	expiry := now.Add(duration)

	if permaCreds.ClientID == "" {
		return nil, errors.New("Temporary credentials cannot be created from credentials that have an empty ClientId")
	}
	if permaCreds.AccessToken == "" {
		return nil, errors.New("Temporary credentials cannot be created from credentials that have an empty AccessToken")
	}
	if permaCreds.Certificate != "" {
		return nil, errors.New("Temporary credentials cannot be created from temporary credentials, only from permanent credentials")
	}

	cert := &Certificate{
		Version:   1,
		Scopes:    scopes,
		Start:     start.UnixNano() / 1e6,
		Expiry:    expiry.UnixNano() / 1e6,
		Seed:      slugid.V4() + slugid.V4(),
		Signature: "", // gets set in Sign() method below
	}
	// include the issuer iff this is a named credential
	if tempClientID != "" {
		cert.Issuer = permaCreds.ClientID
	}

	_ = cert.Sign(permaCreds.AccessToken, tempClientID)

	certBytes, err := json.Marshal(cert)
	if err != nil {
		return
	}

	tempAccessToken, err := generateTemporaryAccessToken(permaCreds.AccessToken, cert.Seed)
	if err != nil {
		return
	}

	tempCreds = &Credentials{
		ClientID:         permaCreds.ClientID,
		AccessToken:      tempAccessToken,
		Certificate:      string(certBytes),
		AuthorizedScopes: permaCreds.AuthorizedScopes,
	}
	if tempClientID != "" {
		tempCreds.ClientID = tempClientID
	}

	return
}

// CreateTemporaryCredentials is an alias for CreateNamedTemporaryCredentials
// with an empty name.
func (permaCreds *Credentials) CreateTemporaryCredentials(duration time.Duration, scopes ...string) (tempCreds *Credentials, err error) {
	return permaCreds.CreateNamedTemporaryCredentials("", duration, scopes...)
}

func (cert *Certificate) Sign(accessToken string, tempClientID string) (err error) {
	lines := []string{"version:" + strconv.Itoa(cert.Version)}
	// iff this is a named credential, include clientId and issuer
	if cert.Issuer != "" {
		lines = append(lines,
			"clientId:"+tempClientID,
			"issuer:"+cert.Issuer,
		)
	}
	lines = append(lines,
		"seed:"+cert.Seed,
		"start:"+strconv.FormatInt(cert.Start, 10),
		"expiry:"+strconv.FormatInt(cert.Expiry, 10),
		"scopes:",
	)
	lines = append(lines, cert.Scopes...)
	hash := hmac.New(sha256.New, []byte(accessToken))
	text := strings.Join(lines, "\n")
	_, err = hash.Write([]byte(text))
	if err != nil {
		return err
	}
	cert.Signature = base64.StdEncoding.EncodeToString(hash.Sum([]byte{}))
	return
}

func generateTemporaryAccessToken(permAccessToken, seed string) (tempAccessToken string, err error) {
	hash := hmac.New(sha256.New, []byte(permAccessToken))
	_, err = hash.Write([]byte(seed))
	if err != nil {
		return "", err
	}
	tempAccessToken = strings.TrimRight(base64.URLEncoding.EncodeToString(hash.Sum([]byte{})), "=")
	return
}

// Cert attempts to parse the certificate string to return it as an object. If
// the certificate is an empty string (e.g. in the case of permanent
// credentials) then a nil pointer is returned for the certificate. If a
// certificate has been specified but cannot be parsed, an error is returned,
// and cert is an empty certificate (rather than nil).
func (creds *Credentials) Cert() (cert *Certificate, err error) {
	if creds.Certificate == "" {
		return
	}
	cert = new(Certificate)
	err = json.Unmarshal([]byte(creds.Certificate), cert)
	return
}

// CredentialsFromEnvVars creates and returns Taskcluster credentials
// initialised from the values of environment variables:
//
//	TASKCLUSTER_CLIENT_ID
//	TASKCLUSTER_ACCESS_TOKEN
//	TASKCLUSTER_CERTIFICATE
//
// No validation is performed on the assigned values, and unset environment
// variables will result in empty string values.
func CredentialsFromEnvVars() *Credentials {
	return &Credentials{
		ClientID:    os.Getenv("TASKCLUSTER_CLIENT_ID"),
		AccessToken: os.Getenv("TASKCLUSTER_ACCESS_TOKEN"),
		Certificate: os.Getenv("TASKCLUSTER_CERTIFICATE"),
	}
}

// RootURLFromEnvVars returns the value of environment variable
// TASKCLUSTER_PROXY_URL if set to a non-empty string, otherwise the value of
// TASKCLUSTER_ROOT_URL if set, otherwise the empty string.
func RootURLFromEnvVars() string {
	if proxyURL := os.Getenv("TASKCLUSTER_PROXY_URL"); proxyURL != "" {
		return proxyURL
	}
	return os.Getenv("TASKCLUSTER_ROOT_URL")
}