Implement Application Default Credentials for the google connector

connector/google/google.go

@@ -71,7 +71,7 @@ func (c *Config) Open(id string, logger log.Logger) (conn connector.Connector, e
 		scopes = append(scopes, "profile", "email")
 	}
 
-	srv, err := createDirectoryService(c.ServiceAccountFilePath, c.AdminEmail)
+	srv, err := createDirectoryService(c.ServiceAccountFilePath, c.AdminEmail, logger)
 	if err != nil {
 		cancel()
 		return nil, fmt.Errorf("could not create directory service: %v", err)
@@ -279,37 +279,37 @@ func (c *googleConnector) getGroups(email string, fetchTransitiveGroupMembership
 	return uniqueGroups(userGroups), nil
 }
 
-// createDirectoryService loads a google service account credentials file,
-// sets up super user impersonation and creates an admin client for calling
-// the google admin api
-func createDirectoryService(serviceAccountFilePath string, email string) (*admin.Service, error) {
-	if serviceAccountFilePath == "" && email == "" {
-		return nil, nil
-	}
-	if serviceAccountFilePath == "" || email == "" {
-		return nil, fmt.Errorf("directory service requires both serviceAccountFilePath and adminEmail")
-	}
-	jsonCredentials, err := os.ReadFile(serviceAccountFilePath)
-	if err != nil {
-		return nil, fmt.Errorf("error reading credentials from file: %v", err)
+// 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) {
+	if email == "" {
+		return nil, fmt.Errorf("directory service requires adminEmail")
 	}
 
-	config, err := google.JWTConfigFromJSON(jsonCredentials, admin.AdminDirectoryGroupReadonlyScope)
-	if err != nil {
-		return nil, fmt.Errorf("unable to parse client secret file to config: %v", err)
-	}
-
-	// Impersonate an admin. This is mandatory for the admin APIs.
-	config.Subject = email
+	var jsonCredentials []byte
+	var err error
 
 	ctx := context.Background()
-	client := config.Client(ctx)
-
-	srv, err := admin.NewService(ctx, option.WithHTTPClient(client))
+	if serviceAccountFilePath == "" {
+		logger.Warn("the application default credential is used since the service account file path is not used")
+		credential, err := google.FindDefaultCredentials(ctx)
+		if err != nil {
+			return nil, fmt.Errorf("failed to fetch application default credentials: %w", err)
+		}
+		jsonCredentials = credential.JSON
+	} else {
+		jsonCredentials, err = os.ReadFile(serviceAccountFilePath)
+		if err != nil {
+			return nil, fmt.Errorf("error reading credentials from file: %v", err)
+		}
+	}
+	config, err := google.JWTConfigFromJSON(jsonCredentials, admin.AdminDirectoryGroupReadonlyScope)
 	if err != nil {
-		return nil, fmt.Errorf("unable to create directory service %v", err)
+		return nil, fmt.Errorf("unable to parse credentials to config: %v", err)
 	}
-	return srv, nil
+	config.Subject = email
+	return admin.NewService(ctx, option.WithHTTPClient(config.Client(ctx)))
 }
 
 // uniqueGroups returns the unique groups of a slice

connector/google/google_test.go

@@ -0,0 +1,145 @@
+package google
+
+import (
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"testing"
+
+	"github.com/sirupsen/logrus"
+	"github.com/stretchr/testify/assert"
+)
+
+func testSetup(t *testing.T) *httptest.Server {
+	mux := http.NewServeMux()
+	// TODO: mock calls
+	// mux.HandleFunc("/admin/directory/v1/groups", func(w http.ResponseWriter, r *http.Request) {
+	// 	w.Header().Add("Content-Type", "application/json")
+	// 	json.NewEncoder(w).Encode(&admin.Groups{
+	// 		Groups: []*admin.Group{},
+	// 	})
+	// })
+	return httptest.NewServer(mux)
+}
+
+func newConnector(config *Config, serverURL string) (*googleConnector, error) {
+	log := logrus.New()
+	conn, err := config.Open("id", log)
+	if err != nil {
+		return nil, err
+	}
+
+	googleConn, ok := conn.(*googleConnector)
+	if !ok {
+		return nil, fmt.Errorf("failed to convert to googleConnector")
+	}
+	return googleConn, nil
+}
+
+func tempServiceAccountKey() (string, error) {
+	fd, err := os.CreateTemp("", "google_service_account_key")
+	if err != nil {
+		return "", err
+	}
+	defer fd.Close()
+	err = json.NewEncoder(fd).Encode(map[string]string{
+		"type":                 "service_account",
+		"project_id":           "sample-project",
+		"private_key_id":       "sample-key-id",
+		"private_key":          "-----BEGIN PRIVATE KEY-----\nsample-key\n-----END PRIVATE KEY-----\n",
+		"client_id":            "sample-client-id",
+		"client_x509_cert_url": "localhost",
+	})
+	return fd.Name(), err
+}
+
+func TestOpen(t *testing.T) {
+	ts := testSetup(t)
+	defer ts.Close()
+
+	type testCase struct {
+		config      *Config
+		expectedErr string
+
+		// string to set in GOOGLE_APPLICATION_CREDENTIALS. As local development environments can
+		// already contain ADC, test cases will be built uppon this setting this env variable
+		adc string
+	}
+
+	serviceAccountFilePath, err := tempServiceAccountKey()
+	assert.Nil(t, err)
+
+	for name, reference := range map[string]testCase{
+		"missing_admin_email": {
+			config: &Config{
+				ClientID:     "testClient",
+				ClientSecret: "testSecret",
+				RedirectURI:  ts.URL + "/callback",
+				Scopes:       []string{"openid", "groups"},
+			},
+			expectedErr: "requires adminEmail",
+		},
+		"service_account_key_not_found": {
+			config: &Config{
+				ClientID:               "testClient",
+				ClientSecret:           "testSecret",
+				RedirectURI:            ts.URL + "/callback",
+				Scopes:                 []string{"openid", "groups"},
+				AdminEmail:             "[email protected]",
+				ServiceAccountFilePath: "not_found.json",
+			},
+			expectedErr: "error reading credentials",
+		},
+		"service_account_key_valid": {
+			config: &Config{
+				ClientID:               "testClient",
+				ClientSecret:           "testSecret",
+				RedirectURI:            ts.URL + "/callback",
+				Scopes:                 []string{"openid", "groups"},
+				AdminEmail:             "[email protected]",
+				ServiceAccountFilePath: serviceAccountFilePath,
+			},
+			expectedErr: "",
+		},
+		"adc": {
+			config: &Config{
+				ClientID:     "testClient",
+				ClientSecret: "testSecret",
+				RedirectURI:  ts.URL + "/callback",
+				Scopes:       []string{"openid", "groups"},
+				AdminEmail:   "[email protected]",
+			},
+			adc:         serviceAccountFilePath,
+			expectedErr: "",
+		},
+		"adc_priority": {
+			config: &Config{
+				ClientID:               "testClient",
+				ClientSecret:           "testSecret",
+				RedirectURI:            ts.URL + "/callback",
+				Scopes:                 []string{"openid", "groups"},
+				AdminEmail:             "[email protected]",
+				ServiceAccountFilePath: serviceAccountFilePath,
+			},
+			adc:         "/dev/null",
+			expectedErr: "",
+		},
+	} {
+		reference := reference
+		t.Run(name, func(t *testing.T) {
+			assert := assert.New(t)
+
+			os.Setenv("GOOGLE_APPLICATION_CREDENTIALS", reference.adc)
+			conn, err := newConnector(reference.config, ts.URL)
+
+			if reference.expectedErr == "" {
+				assert.Nil(err)
+				assert.NotNil(conn)
+			} else {
+				assert.ErrorContains(err, reference.expectedErr)
+			}
+		})
+	}
+}