git-ecosystem/git-credential-manager · error · ArgumentOutOfRangeException

Unknown authentication mode

Error message

Unknown authentication mode

What it means

The Bitbucket UI credential prompt switch handles a fixed set of AuthenticationModes values; any mode selected outside the handled cases hits the default branch and throws ArgumentOutOfRangeException with message 'Unknown authentication mode'. This is an internal invariant: the UI should only ever offer supported modes.

Solutions

1. Ensure only single, supported modes (Basic, OAuth/Browser, Gcm) are included in the modes set passed to GetCredentialsAsync
2. Update Git Credential Manager to matching versions so UI helper and enum definitions agree
3. If custom-calling, avoid passing combined flags; pass one mode per prompt

Example fix

// before
var result = await auth.GetCredentialsAsync(uri, null, AuthenticationModes.Basic | AuthenticationModes.OAuth | (AuthenticationModes)0x100);
// after
var result = await auth.GetCredentialsAsync(uri, null, AuthenticationModes.Basic | AuthenticationModes.OAuth);

var allowed = new[] { AuthenticationModes.Basic, AuthenticationModes.OAuth, AuthenticationModes.Browser };
if (!allowed.Contains(mode)) throw new InvalidOperationException($"Unsupported mode {mode}");

bool IsSupportedMode(AuthenticationModes m) => m is AuthenticationModes.Basic or AuthenticationModes.OAuth or AuthenticationModes.Browser;

try { await auth.GetCredentialsAsync(uri, user, modes); }
catch (ArgumentOutOfRangeException ex) { trace.Error(ex); return null; }

When it happens

Trigger: GetCredentialsAsync -> GetCredentialsViaUiAsync when viewModel.SelectedMode holds a mode value not present in the switch's case labels (e.g. an enum value added or combined flags passed through).

Common situations: Version mismatch between GCM components or plugins passing a new/combined AuthenticationModes value; manual construction of CredentialsPromptOptions with an unhandled mode.

Understand the failure class

Background: Invalid enum value errors: "Unknown type", "Invalid scope", "must be one of" — when a string is not on the library's allowed list — this error's family across 23 libraries.

• Authentication and authorization failures — expired tokens, bad credentials, and missing scopes.

Related errors

• Unexpected AuthenticationModes returned from prompt
• Unexpected interaction mode.
• At least one AuthenticationModes must be supplied
• Unsupported workload federation scenario.
• No protocol name mapping is defined for the given…

AI-assisted analysis of git-ecosystem/git-credential-manager@e8ce762cd0 (2026-09-11). Data as JSON: /api/errors/c2e995c6879e51eb. Report an issue: GitHub.

Appendix: source

Thrown at src/Atlassian.Bitbucket/BitbucketAuthentication.cs:145

            }

            await AvaloniaUi.ShowViewAsync<CredentialsView>(viewModel, GetParentWindowHandle(), CancellationToken.None);

            ThrowIfWindowCancelled(viewModel);

            switch (viewModel.SelectedMode)
            {
                case AuthenticationModes.OAuth:
                    return new CredentialsPromptResult(AuthenticationModes.OAuth);

                case AuthenticationModes.Basic:
                    return new CredentialsPromptResult(
                        AuthenticationModes.Basic,
                        new GitCredential(viewModel.UserName, viewModel.Password)
                        );

                default:
                    throw new ArgumentOutOfRangeException(nameof(AuthenticationModes),
                        "Unknown authentication mode", viewModel.SelectedMode.ToString());
            }
        }

        private async Task<CredentialsPromptResult> GetCredentialsViaTtyAsync(Uri targetUri, string userName, AuthenticationModes modes)
        {
            ThrowIfTerminalPromptsDisabled();

            switch (modes)
            {
                case AuthenticationModes.Basic:
                    Context.Console.WriteLine($"Enter Bitbucket credentials for '{targetUri}'...");

                    if (!string.IsNullOrWhiteSpace(userName))
                    {
                        // Don't need to prompt for the username if it has been specified already
                        Context.Console.WriteLine($"Username: {userName}");
                    }

View on GitHub (pinned to e8ce762cd0)