The CredUIConfirmCredentials function is called after CredUIPromptForCredentials or CredUICmdLinePromptForCredentials, to confirm the validity of the credential harvested.

[DllImport("credui.dll", EntryPoint="CredUIConfirmCredentialsW", CharSet = CharSet.Unicode)]

private static extern CredUIReturnCodes CredUIConfirmCredentials( string targetName, [MarshalAs(UnmanagedType.Bool)] bool confirm);