fix: allow credentials discovery to be optional

Allow the user to configure the helper such that failure to find the required environment variables results in an empty username and password being returned instead of causing the helper to fail.

helper/env.go

@@ -19,15 +19,27 @@ var nonAlphanumericPattern = regexp.MustCompile(`[^a-zA-Z0-9]`)
 var _ credentials.Helper = EnvHelper{}
 
 type EnvHelper struct {
+	CredentialsOptional bool
 }
 
+// Get retrieves the credentials for the server URL from the process
+// environment.
 func (e EnvHelper) Get(serverURL string) (string, string, error) {
 	logger := slog.Default().With("action", "get", "serverURL", serverURL)
 
-	// FIXME: allow this to return empty on failure if so configured
 	user, password, err := credentialsForServer(serverURL)
 
-	logger.Info("Get", "user", user, "err", err)
+	if err != nil {
+		if e.CredentialsOptional {
+			logger.Warn("Ignoring failed credential lookup, unset DOCKER_CREDENTIALS_ENV_OPTIONAL if this should cause Docker to fail", "err", err)
+			return "", "", nil
+		}
+
+		logger.Error("Failed to retrieve credentials, set DOCKER_CREDENTIALS_ENV_OPTIONAL to ignore this error.", "err", err)
+		return "", "", err
+	}
+
+	logger.Info("Got credentials from environment", "user", user, "err", err)
 
 	return user, password, err
 }
@@ -43,8 +55,7 @@ func (e EnvHelper) Delete(serverURL string) error {
 }
 
 func (e EnvHelper) List() (map[string]string, error) {
-	slog.Info("", "action", "list")
-
+	slog.Error("List action not implemented", "action", "list")
 	return nil, ErrNotImplemented
 }
 

helper/env_test.go

@@ -21,6 +21,17 @@ func TestEnvHelper_Get_Success(t *testing.T) {
 	assert.Equal(t, "testpassword", password)
 }
 
+func TestEnvHelper_Get_CredentialsOptional_Success(t *testing.T) {
+
+	helper := EnvHelper{CredentialsOptional: true}
+
+	user, password, err := helper.Get("example.com")
+
+	assert.NoError(t, err)
+	assert.Empty(t, user)
+	assert.Empty(t, password)
+}
+
 func TestEnvHelper_Get_Failure(t *testing.T) {
 	helper := EnvHelper{}
 

main.go

@@ -21,7 +21,9 @@ func main() {
 
 	configureLogging()
 
-	credentials.Serve(helper.EnvHelper{})
+	credentialsOptional := os.Getenv("DOCKER_CREDENTIALS_ENV_OPTIONAL") == "true"
+
+	credentials.Serve(helper.EnvHelper{CredentialsOptional: credentialsOptional})
 }
 
 func configureLogging() {