grpc/grpc-go · error

credentials: failed to read the service account key file: %v

Error message

credentials: failed to read the service account key file: %v

What it means

Returned by oauth.NewJWTAccessFromFile (oauth.go:78) when os.ReadFile(keyFile) fails. The function loads a Google service-account JSON key file to build self-signed JWT access credentials; without readable file contents it cannot proceed. The wrapped %v carries the underlying os PathError (open … no such file or directory / permission denied).

Source

Thrown at credentials/oauth/oauth.go:78

// removeServiceNameFromJWTURI removes RPC service name from URI.
func removeServiceNameFromJWTURI(uri string) (string, error) {
	parsed, err := url.Parse(uri)
	if err != nil {
		return "", err
	}
	parsed.Path = "/"
	return parsed.String(), nil
}

type jwtAccess struct {
	jsonKey []byte
}

// NewJWTAccessFromFile creates PerRPCCredentials from the given keyFile.
func NewJWTAccessFromFile(keyFile string) (credentials.PerRPCCredentials, error) {
	jsonKey, err := os.ReadFile(keyFile)
	if err != nil {
		return nil, fmt.Errorf("credentials: failed to read the service account key file: %v", err)
	}
	return NewJWTAccessFromKey(jsonKey)
}

// NewJWTAccessFromKey creates PerRPCCredentials from the given jsonKey.
func NewJWTAccessFromKey(jsonKey []byte) (credentials.PerRPCCredentials, error) {
	return jwtAccess{jsonKey}, nil
}

func (j jwtAccess) GetRequestMetadata(ctx context.Context, uri ...string) (map[string]string, error) {
	// Remove RPC service name from URI that will be used as audience
	// in a self-signed JWT token. It follows https://google.aip.dev/auth/4111.
	aud, err := removeServiceNameFromJWTURI(uri[0])
	if err != nil {
		return nil, err
	}
	// TODO: the returned TokenSource is reusable. Store it in a sync.Map, with
	// uri as the key, to avoid recreating for every RPC.

View on GitHub (pinned to 03255a9237)

Solutions

1. Verify the path exists and is readable (os.Stat / ls -l) from the process's working directory.
2. Use an absolute path; mount the key file via the same mechanism (secret/configmap) the deployment uses.
3. Prefer NewJWTAccessFromKey([]byte) and pass already-loaded bytes if the path resolution is fragile.

Example fix

// before
creds, err := oauth.NewJWTAccessFromFile("service-account.json") // relative, cwd-dependent

// after
const keyPath = "/etc/secrets/sa/service-account.json"
if _, err := os.Stat(keyPath); err != nil {
    log.Fatalf("key file: %v", err)
}
creds, err := oauth.NewJWTAccessFromFile(keyPath)

if keyPath == "" { return fmt.Errorf("service-account key path is empty") }
if _, err := os.Stat(keyPath); err != nil {
    return fmt.Errorf("service-account key not found: %w", err)
}
creds, err := oauth.NewJWTAccessFromFile(keyPath)
if err != nil { return err }

creds, err := oauth.NewJWTAccessFromFile(keyPath)
if err != nil {
    if strings.Contains(err.Error(), "failed to read the service account key file") {
        // surface actionable message: check path/permissions/mount
    }
    return err
}

When it happens

Trigger: Passing a non-existent, relative, or unreadable path to NewJWTAccessFromFile; the file exists but the process lacks read permission; path derived from a missing config flag.

Common situations: Service-account JSON not mounted in the container; typo in GOOGLE_APPLICATION_CREDENTIALS-style path; running as a different UID than the file owner; relative path interpreted from an unexpected working directory.

Related errors

• tokenFilePath cannot be empty
• unable to transfer jwtAccess PerRPCCredentials: %v
• credentials: failed to append certificates
• token file access error
• credentials: audience cannot be empty

AI-assisted analysis of grpc/grpc-go@03255a9237 (2026-08-07). Data as JSON: /api/errors/9af7234d98c9b919. Report an issue: GitHub.