google: adding support for external account authorized user

To support a new type of credential: `ExternalAccountAuthorizedUser`

* Refactor the common dependency STS to a separate package.
* Adding the `externalaccountauthorizeduser` package.

Change-Id: I9b9624f912d216b67a0d31945a50f057f747710b
GitHub-Last-Rev: 6e2aaff345
GitHub-Pull-Request: golang/oauth2#671
Reviewed-on: https://go-review.googlesource.com/c/oauth2/+/531095
Reviewed-by: Leo Siracusa <leosiracusa@google.com>
Reviewed-by: Alex Eitzman <eitzman@google.com>
Run-TryBot: Cody Oss <codyoss@google.com>
Reviewed-by: Cody Oss <codyoss@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

google/google.go

@@ -16,6 +16,7 @@ import (
 	"cloud.google.com/go/compute/metadata"
 	"golang.org/x/oauth2"
 	"golang.org/x/oauth2/google/internal/externalaccount"
+	"golang.org/x/oauth2/google/internal/externalaccountauthorizeduser"
 	"golang.org/x/oauth2/jwt"
 )
 
@@ -96,10 +97,11 @@ func JWTConfigFromJSON(jsonKey []byte, scope ...string) (*jwt.Config, error) {
 
 // JSON key file types.
 const (
-	serviceAccountKey          = "service_account"
-	userCredentialsKey         = "authorized_user"
-	externalAccountKey         = "external_account"
-	impersonatedServiceAccount = "impersonated_service_account"
+	serviceAccountKey                = "service_account"
+	userCredentialsKey               = "authorized_user"
+	externalAccountKey               = "external_account"
+	externalAccountAuthorizedUserKey = "external_account_authorized_user"
+	impersonatedServiceAccount       = "impersonated_service_account"
 )
 
 // credentialsFile is the unmarshalled representation of a credentials file.
@@ -132,6 +134,9 @@ type credentialsFile struct {
 	QuotaProjectID                 string                           `json:"quota_project_id"`
 	WorkforcePoolUserProject       string                           `json:"workforce_pool_user_project"`
 
+	// External Account Authorized User fields
+	RevokeURL string `json:"revoke_url"`
+
 	// Service account impersonation
 	SourceCredentials *credentialsFile `json:"source_credentials"`
 }
@@ -200,6 +205,19 @@ func (f *credentialsFile) tokenSource(ctx context.Context, params CredentialsPar
 			WorkforcePoolUserProject: f.WorkforcePoolUserProject,
 		}
 		return cfg.TokenSource(ctx)
+	case externalAccountAuthorizedUserKey:
+		cfg := &externalaccountauthorizeduser.Config{
+			Audience:       f.Audience,
+			RefreshToken:   f.RefreshToken,
+			TokenURL:       f.TokenURLExternal,
+			TokenInfoURL:   f.TokenInfoURL,
+			ClientID:       f.ClientID,
+			ClientSecret:   f.ClientSecret,
+			RevokeURL:      f.RevokeURL,
+			QuotaProjectID: f.QuotaProjectID,
+			Scopes:         params.Scopes,
+		}
+		return cfg.TokenSource(ctx)
 	case impersonatedServiceAccount:
 		if f.ServiceAccountImpersonationURL == "" || f.SourceCredentials == nil {
 			return nil, errors.New("missing 'source_credentials' field or 'service_account_impersonation_url' in credentials")