Google: Implement groups fetch by default service account from metadata (support for GKE workload identity)

connector/google/google.go

@@ -10,11 +10,13 @@ import (
 	"strings"
 	"time"
 
+	"cloud.google.com/go/compute/metadata"
 	"github.com/coreos/go-oidc/v3/oidc"
 	"golang.org/x/exp/slices"
 	"golang.org/x/oauth2"
 	"golang.org/x/oauth2/google"
 	admin "google.golang.org/api/admin/directory/v1"
+	"google.golang.org/api/impersonate"
 	"google.golang.org/api/option"
 
 	"github.com/dexidp/dex/connector"
@@ -94,8 +96,7 @@ func (c *Config) Open(id string, logger log.Logger) (conn connector.Connector, e
 		return nil, fmt.Errorf("directory service requires the domainToAdminEmail option to be configured")
 	}
 
-	// Fixing a regression caused by default config fallback: https://github.com/dexidp/dex/issues/2699
-	if (c.ServiceAccountFilePath != "" && len(c.DomainToAdminEmail) > 0) || slices.Contains(scopes, "groups") {
+	if (len(c.DomainToAdminEmail) > 0) || slices.Contains(scopes, "groups") {
 		for domain, adminEmail := range c.DomainToAdminEmail {
 			srv, err := createDirectoryService(c.ServiceAccountFilePath, adminEmail, logger)
 			if err != nil {
@@ -350,25 +351,83 @@ func (c *googleConnector) extractDomainFromEmail(email string) string {
 	return wildcardDomainToAdminEmail
 }
 
+// getCredentialsFromFilePath reads and returns the service account credentials from the file at the provided path.
+// If an error occurs during the read, it is returned.
+func getCredentialsFromFilePath(serviceAccountFilePath string) ([]byte, error) {
+	jsonCredentials, err := os.ReadFile(serviceAccountFilePath)
+	if err != nil {
+		return nil, fmt.Errorf("error reading credentials from file: %v", err)
+	}
+	return jsonCredentials, nil
+}
+
+// getCredentialsFromDefault retrieves the application's default credentials.
+// If the default credential is empty, it attempts to create a new service with metadata credentials.
+// If successful, it returns the service and nil error.
+// If unsuccessful, it returns the error and a nil service.
+func getCredentialsFromDefault(ctx context.Context, email string, logger log.Logger) ([]byte, *admin.Service, error) {
+	credential, err := google.FindDefaultCredentials(ctx)
+	if err != nil {
+		return nil, nil, fmt.Errorf("failed to fetch application default credentials: %w", err)
+	}
+
+	if credential.JSON == nil {
+		logger.Info("JSON is empty, using flow for GCE")
+		service, err := createServiceWithMetadataServer(ctx, email, logger)
+		if err != nil {
+			return nil, nil, err
+		}
+		return nil, service, nil
+	}
+
+	return credential.JSON, nil, nil
+}
+
+// createServiceWithMetadataServer creates a new service using metadata server.
+// If an error occurs during the process, it is returned along with a nil service.
+func createServiceWithMetadataServer(ctx context.Context, adminEmail string, logger log.Logger) (*admin.Service, error) {
+	serviceAccountEmail, err := metadata.Email("default")
+	logger.Infof("discovered serviceAccountEmail: %s", serviceAccountEmail)
+
+	if err != nil {
+		return nil, fmt.Errorf("unable to get service account email from metadata server: %v", err)
+	}
+
+	config := impersonate.CredentialsConfig{
+		TargetPrincipal: serviceAccountEmail,
+		Scopes:          []string{admin.AdminDirectoryGroupReadonlyScope},
+		Lifetime:        0,
+		Subject:         adminEmail,
+	}
+
+	tokenSource, err := impersonate.CredentialsTokenSource(ctx, config)
+	if err != nil {
+		return nil, fmt.Errorf("unable to impersonate with %s, error: %v", adminEmail, err)
+	}
+
+	return admin.NewService(ctx, option.WithHTTPClient(oauth2.NewClient(ctx, tokenSource)))
+}
+
 // createDirectoryService sets up super user impersonation and creates an admin client for calling
 // the google admin api. If no serviceAccountFilePath is defined, the application default credential
 // is used.
-func createDirectoryService(serviceAccountFilePath, email string, logger log.Logger) (*admin.Service, error) {
+func createDirectoryService(serviceAccountFilePath, email string, logger log.Logger) (service *admin.Service, err error) {
 	var jsonCredentials []byte
-	var err error
 
 	ctx := context.Background()
 	if serviceAccountFilePath == "" {
 		logger.Warn("the application default credential is used since the service account file path is not used")
-		credential, err := google.FindDefaultCredentials(ctx)
+		jsonCredentials, service, err = getCredentialsFromDefault(ctx, email, logger)
 		if err != nil {
-			return nil, fmt.Errorf("failed to fetch application default credentials: %w", err)
+			return
+		}
+		if service != nil {
+			return
 		}
-		jsonCredentials = credential.JSON
 	} else {
-		jsonCredentials, err = os.ReadFile(serviceAccountFilePath)
+		jsonCredentials, err = getCredentialsFromFilePath(serviceAccountFilePath)
 		if err != nil {
-			return nil, fmt.Errorf("error reading credentials from file: %v", err)
+			return
 		}
 	}
 	config, err := google.JWTConfigFromJSON(jsonCredentials, admin.AdminDirectoryGroupReadonlyScope)

connector/google/google_test.go

@@ -7,6 +7,7 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"os"
+	"strings"
 	"testing"
 
 	"github.com/sirupsen/logrus"
@@ -291,3 +292,100 @@ func TestDomainToAdminEmailConfig(t *testing.T) {
 		})
 	}
 }
+
+var gceMetadataFlags = map[string]bool{
+	"failOnEmailRequest": false,
+}
+
+func mockGCEMetadataServer() *httptest.Server {
+	mux := http.NewServeMux()
+
+	mux.HandleFunc("/computeMetadata/v1/instance/service-accounts/default/email", func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Add("Content-Type", "application/json")
+		if gceMetadataFlags["failOnEmailRequest"] {
+			w.WriteHeader(http.StatusBadRequest)
+		}
+		json.NewEncoder(w).Encode("[email protected]")
+	})
+	mux.HandleFunc("/computeMetadata/v1/instance/service-accounts/default/token", func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Add("Content-Type", "application/json")
+		json.NewEncoder(w).Encode(struct {
+			AccessToken  string `json:"access_token"`
+			ExpiresInSec int    `json:"expires_in"`
+			TokenType    string `json:"token_type"`
+		}{
+			AccessToken:  "my-example.token",
+			ExpiresInSec: 3600,
+			TokenType:    "Bearer",
+		})
+	})
+
+	return httptest.NewServer(mux)
+}
+
+func TestGCEWorkloadIdentity(t *testing.T) {
+	ts := testSetup()
+	defer ts.Close()
+
+	metadataServer := mockGCEMetadataServer()
+	defer metadataServer.Close()
+	metadataServerHost := strings.Replace(metadataServer.URL, "http://", "", 1)
+
+	os.Setenv("GCE_METADATA_HOST", metadataServerHost)
+	os.Setenv("GOOGLE_APPLICATION_CREDENTIALS", "")
+	os.Setenv("HOME", "/tmp")
+
+	gceMetadataFlags["failOnEmailRequest"] = true
+	_, err := newConnector(&Config{
+		ClientID:           "testClient",
+		ClientSecret:       "testSecret",
+		RedirectURI:        ts.URL + "/callback",
+		Scopes:             []string{"openid", "groups"},
+		DomainToAdminEmail: map[string]string{"dexidp.com": "[email protected]"},
+	})
+	assert.Error(t, err)
+
+	gceMetadataFlags["failOnEmailRequest"] = false
+	conn, err := newConnector(&Config{
+		ClientID:           "testClient",
+		ClientSecret:       "testSecret",
+		RedirectURI:        ts.URL + "/callback",
+		Scopes:             []string{"openid", "groups"},
+		DomainToAdminEmail: map[string]string{"dexidp.com": "[email protected]"},
+	})
+	assert.Nil(t, err)
+
+	conn.adminSrv["dexidp.com"], err = admin.NewService(context.Background(), option.WithoutAuthentication(), option.WithEndpoint(ts.URL))
+	assert.Nil(t, err)
+	type testCase struct {
+		userKey     string
+		expectedErr string
+	}
+
+	for name, testCase := range map[string]testCase{
+		"correct_user_request": {
+			userKey:     "[email protected]",
+			expectedErr: "",
+		},
+		"wrong_user_request": {
+			userKey:     "[email protected]",
+			expectedErr: "unable to find super admin email",
+		},
+		"wrong_connector_response": {
+			userKey:     "user_1_foo.bar",
+			expectedErr: "unable to find super admin email",
+		},
+	} {
+		t.Run(name, func(t *testing.T) {
+			assert := assert.New(t)
+			lookup := make(map[string]struct{})
+
+			_, err := conn.getGroups(testCase.userKey, true, lookup)
+			if testCase.expectedErr != "" {
+				assert.ErrorContains(err, testCase.expectedErr)
+			} else {
+				assert.Nil(err)
+			}
+		})
+	}
+}

go.mod

@@ -3,6 +3,7 @@ module github.com/dexidp/dex
 go 1.20
 
 require (
+	cloud.google.com/go/compute/metadata v0.2.3
 	entgo.io/ent v0.12.3
 	github.com/AppsFlyer/go-sundheit v0.5.0
 	github.com/Masterminds/semver v1.5.0
@@ -43,7 +44,6 @@ require (
 require (
 	ariga.io/atlas v0.10.2-0.20230427182402-87a07dfb83bf // indirect
 	cloud.google.com/go/compute v1.19.3 // indirect
-	cloud.google.com/go/compute/metadata v0.2.3 // indirect
 	github.com/Azure/go-ntlmssp v0.0.0-20220621081337-cb9428e4ac1e // indirect
 	github.com/Masterminds/goutils v1.1.1 // indirect
 	github.com/Masterminds/semver/v3 v3.2.0 // indirect