ci-9739 - workload identity/OIDC support for GAR/GCR (#413)

* adds support for oidc access tokens gar/gcr

cmd/drone-docker/main.go

@@ -292,6 +292,11 @@ func main() {
 			Usage:  "registry type",
 			EnvVar: "PLUGIN_REGISTRY_TYPE",
 		},
+		cli.StringFlag{
+			Name:   "access-token",
+			Usage:  "access token",
+			EnvVar: "ACCESS_TOKEN",
+		},
 	}
 
 	if err := app.Run(os.Args); err != nil {
@@ -309,11 +314,12 @@ func run(c *cli.Context) error {
 		Dryrun:  c.Bool("dry-run"),
 		Cleanup: c.BoolT("docker.purge"),
 		Login: docker.Login{
-			Registry: c.String("docker.registry"),
-			Username: c.String("docker.username"),
-			Password: c.String("docker.password"),
-			Email:    c.String("docker.email"),
-			Config:   c.String("docker.config"),
+			Registry:    c.String("docker.registry"),
+			Username:    c.String("docker.username"),
+			Password:    c.String("docker.password"),
+			Email:       c.String("docker.email"),
+			Config:      c.String("docker.config"),
+			AccessToken: c.String("access-token"),
 		},
 		CardPath:     c.String("drone-card-path"),
 		ArtifactFile: c.String("artifact-file"),

cmd/drone-gcr/main.go

@@ -11,11 +11,15 @@ import (
 	"strconv"
 	"strings"
 
+	docker "github.com/drone-plugins/drone-docker"
+
 	"github.com/joho/godotenv"
 	"github.com/sirupsen/logrus"
+	"golang.org/x/oauth2"
 	"golang.org/x/oauth2/google"
-
-	docker "github.com/drone-plugins/drone-docker"
+	"google.golang.org/api/iamcredentials/v1"
+	"google.golang.org/api/option"
+	"google.golang.org/api/sts/v1"
 )
 
 type Config struct {
@@ -25,11 +29,21 @@ type Config struct {
 	WorkloadIdentity bool
 	Username         string
 	RegistryType     string
+	AccessToken      string
+}
+
+type staticTokenSource struct {
+	token *oauth2.Token
+}
+
+func (s *staticTokenSource) Token() (*oauth2.Token, error) {
+	return s.token, nil
 }
 
 func loadConfig() Config {
 	// Default username
 	username := "_json_key"
+	var config Config
 
 	// Load env-file if it exists
 	if env := os.Getenv("PLUGIN_ENV_FILE"); env != "" {
@@ -38,18 +52,36 @@ func loadConfig() Config {
 		}
 	}
 
+	idToken := getenv("PLUGIN_OIDC_TOKEN_ID")
+	projectId := getenv("PLUGIN_PROJECT_NUMBER")
+	poolId := getenv("PLUGIN_POOL_ID")
+	providerId := getenv("PLUGIN_PROVIDER_ID")
+	serviceAccountEmail := getenv("PLUGIN_SERVICE_ACCOUNT_EMAIL")
+
+	if idToken != "" && projectId != "" && poolId != "" && providerId != "" && serviceAccountEmail != "" {
+		federalToken, err := getFederalToken(idToken, projectId, poolId, providerId)
+		if err != nil {
+			logrus.Fatalf("Error (getFederalToken): %s", err)
+		}
+		accessToken, err := getGoogleCloudAccessToken(federalToken, serviceAccountEmail)
+		if err != nil {
+			logrus.Fatalf("Error (getGoogleCloudAccessToken): %s", err)
+		}
+		config.AccessToken = accessToken
+	} else {
+		password := getenv(
+			"PLUGIN_JSON_KEY",
+			"GCR_JSON_KEY",
+			"GOOGLE_CREDENTIALS",
+			"TOKEN",
+		)
+		config.WorkloadIdentity = parseBoolOrDefault(false, getenv("PLUGIN_WORKLOAD_IDENTITY"))
+		config.Username, config.Password = setUsernameAndPassword(username, password, config.WorkloadIdentity)
+	}
+
 	location := getenv("PLUGIN_LOCATION")
 	repo := getenv("PLUGIN_REPO")
 
-	password := getenv(
-		"PLUGIN_JSON_KEY",
-		"GCR_JSON_KEY",
-		"GOOGLE_CREDENTIALS",
-		"TOKEN",
-	)
-	workloadIdentity := parseBoolOrDefault(false, getenv("PLUGIN_WORKLOAD_IDENTITY"))
-	username, password = setUsernameAndPassword(username, password, workloadIdentity)
-
 	registryType := getenv("PLUGIN_REGISTRY_TYPE")
 	if registryType == "" {
 		registryType = "GCR"
@@ -73,24 +105,23 @@ func loadConfig() Config {
 	if !strings.HasPrefix(repo, registry) {
 		repo = path.Join(registry, repo)
 	}
-
-	return Config{
-		Repo:             repo,
-		Registry:         registry,
-		Password:         password,
-		WorkloadIdentity: workloadIdentity,
-		Username:         username,
-		RegistryType:     registryType,
-	}
+	config.Repo = repo
+	config.Registry = registry
+	config.RegistryType = registryType
+	return config
 }
 
 func main() {
 	config := loadConfig()
+	if config.AccessToken != "" {
+		os.Setenv("ACCESS_TOKEN", config.AccessToken)
+	} else if config.Username != "" && config.Password != "" {
+		os.Setenv("DOCKER_USERNAME", config.Username)
+		os.Setenv("DOCKER_PASSWORD", config.Password)
+	}
 
 	os.Setenv("PLUGIN_REPO", config.Repo)
 	os.Setenv("PLUGIN_REGISTRY", config.Registry)
-	os.Setenv("DOCKER_USERNAME", config.Username)
-	os.Setenv("DOCKER_PASSWORD", config.Password)
 	os.Setenv("PLUGIN_REGISTRY_TYPE", config.RegistryType)
 
 	// invoke the base docker plugin binary
@@ -152,3 +183,49 @@ func getenv(key ...string) (s string) {
 	}
 	return
 }
+
+func getFederalToken(idToken, projectNumber, poolId, providerId string) (string, error) {
+	ctx := context.Background()
+	stsService, err := sts.NewService(ctx, option.WithoutAuthentication())
+	if err != nil {
+		return "", err
+	}
+	audience := fmt.Sprintf("//iam.googleapis.com/projects/%s/locations/global/workloadIdentityPools/%s/providers/%s", projectNumber, poolId, providerId)
+	tokenRequest := &sts.GoogleIdentityStsV1ExchangeTokenRequest{
+		GrantType:          "urn:ietf:params:oauth:grant-type:token-exchange",
+		SubjectToken:       idToken,
+		Audience:           audience,
+		Scope:              "https://www.googleapis.com/auth/cloud-platform",
+		RequestedTokenType: "urn:ietf:params:oauth:token-type:access_token",
+		SubjectTokenType:   "urn:ietf:params:oauth:token-type:id_token",
+	}
+	tokenResponse, err := stsService.V1.Token(tokenRequest).Do()
+	if err != nil {
+		return "", err
+	}
+
+	return tokenResponse.AccessToken, nil
+}
+
+func getGoogleCloudAccessToken(federatedToken string, serviceAccountEmail string) (string, error) {
+	ctx := context.Background()
+	tokenSource := &staticTokenSource{
+		token: &oauth2.Token{AccessToken: federatedToken},
+	}
+	service, err := iamcredentials.NewService(ctx, option.WithTokenSource(tokenSource))
+	if err != nil {
+		return "", err
+	}
+
+	name := "projects/-/serviceAccounts/" + serviceAccountEmail
+	rb := &iamcredentials.GenerateAccessTokenRequest{
+		Scope: []string{"https://www.googleapis.com/auth/cloud-platform"},
+	}
+
+	resp, err := service.Projects.ServiceAccounts.GenerateAccessToken(name, rb).Do()
+	if err != nil {
+		return "", err
+	}
+
+	return resp.AccessToken, nil
+}