Prompt user for name and password with windows cred API

PromptForUserCredentials.cs

private static NetworkCredential PromptForUserCredentials(string preferredUserName, Uri serverUri)
{
    Unmanaged.CREDUI_INFO uiInfo = new Unmanaged.CREDUI_INFO()
    {
        cbSize = Marshal.SizeOf(typeof(Unmanaged.CREDUI_INFO)),
        pszCaptionText = serverUri.Host,
        pszMessageText = string.Format(Resources.DeployWebResources_CredentialPromptMessage, serverUri.Host)
    };

    uint autoPackage = 0;
    IntPtr outCredBuffer;
    uint outCredSize;
    bool save = false;

    int CREDUIWIN_AUTHPACKAGE_ONLY = 0x10;
    uint CRED_PACK_PROTECTED_CREDENTIALS = 0x1;

    uint ret = Unmanaged.CredUIPromptForWindowsCredentials(ref uiInfo, 0, ref autoPackage, IntPtr.Zero, 0, out outCredBuffer, out outCredSize, ref save, CREDUIWIN_AUTHPACKAGE_ONLY);
    if (ret == 0)
    {
        // todo: call two times without hard-code value.
        StringBuilder userName = new StringBuilder(256);
        uint cchUserName = 256;
        StringBuilder password = new StringBuilder(256);
        uint cchPassword = 256;
        StringBuilder domain = new StringBuilder(256);
        uint cchDomain = 256;

        ret = Unmanaged.CredUnPackAuthenticationBuffer(CRED_PACK_PROTECTED_CREDENTIALS, outCredBuffer, outCredSize, userName, ref cchUserName, domain, ref cchDomain, password, ref cchPassword);
        if (ret != 0)
        {
            userName.Length = (int)cchUserName;
            password.Length = (int)cchPassword;
            domain.Length = (int)cchDomain;

            return new NetworkCredential(userName.ToString(), password.ToString(), domain.ToString());
        }
    }

    return null;
}