CredentialUI.cs

using System;
using System.Net;
using System.Runtime.InteropServices;
using System.Text;

namespace SMM.Helper
{
    public static class CredentialsUI
    {
        [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
        private struct CREDUI_INFO
        {
            public int cbSize;
            public IntPtr hwndParent;
            public string pszMessageText;
            public string pszCaptionText;
            public IntPtr hbmBanner;
        }

        [Flags]
        private enum PromptForWindowsCredentialsFlags
        {
            /// <summary>
            /// The caller is requesting that the credential provider return the user name and password in plain text.
            /// This value cannot be combined with SECURE_PROMPT.
            /// </summary>
            CREDUIWIN_GENERIC = 0x1,
            /// <summary>
            /// The Save check box is displayed in the dialog box.
            /// </summary>
            CREDUIWIN_CHECKBOX = 0x2,
            /// <summary>
            /// Only credential providers that support the authentication package specified by the authPackage parameter should be enumerated.
            /// This value cannot be combined with CREDUIWIN_IN_CRED_ONLY.
            /// </summary>
            CREDUIWIN_AUTHPACKAGE_ONLY = 0x10,
            /// <summary>
            /// Only the credentials specified by the InAuthBuffer parameter for the authentication package specified by the authPackage parameter should be enumerated.
            /// If this flag is set, and the InAuthBuffer parameter is NULL, the function fails.
            /// This value cannot be combined with CREDUIWIN_AUTHPACKAGE_ONLY.
            /// </summary>
            CREDUIWIN_IN_CRED_ONLY = 0x20,
            /// <summary>
            /// Credential providers should enumerate only administrators. This value is intended for User Account Control (UAC) purposes only. We recommend that external callers not set this flag.
            /// </summary>
            CREDUIWIN_ENUMERATE_ADMINS = 0x100,
            /// <summary>
            /// Only the incoming credentials for the authentication package specified by the authPackage parameter should be enumerated.
            /// </summary>
            CREDUIWIN_ENUMERATE_CURRENT_USER = 0x200,
            /// <summary>
            /// The credential dialog box should be displayed on the secure desktop. This value cannot be combined with CREDUIWIN_GENERIC.
            /// Windows Vista: This value is not supported until Windows Vista with SP1.
            /// </summary>
            CREDUIWIN_SECURE_PROMPT = 0x1000,
            /// <summary>
            /// The credential provider should align the credential BLOB pointed to by the refOutAuthBuffer parameter to a 32-bit boundary, even if the provider is running on a 64-bit system.
            /// </summary>
            CREDUIWIN_PACK_32_WOW = 0x10000000,
        }

        [DllImport("ole32.dll")]
        private static extern void CoTaskMemFree(IntPtr ptr);

        [DllImport("credui.dll", CharSet = CharSet.Unicode, SetLastError = true)]
        private static extern Boolean CredPackAuthenticationBuffer(
          int dwFlags,
          string pszUserName,
          string pszPassword,
          IntPtr pPackedCredentials,
          ref int pcbPackedCredentials);

        [DllImport("credui.dll", CharSet = CharSet.Unicode)]
        private static extern uint CredUIPromptForWindowsCredentials(ref CREDUI_INFO notUsedHere,
          int authError,
          ref uint authPackage,
          IntPtr InAuthBuffer,
          uint InAuthBufferSize,
          out IntPtr refOutAuthBuffer,
          out uint refOutAuthBufferSize,
          ref bool fSave,
          PromptForWindowsCredentialsFlags flags);

        [DllImport("credui.dll", CharSet = CharSet.Auto)]
        private static extern bool CredUnPackAuthenticationBuffer(int dwFlags, 
            IntPtr pAuthBuffer, uint cbAuthBuffer, 
            StringBuilder pszUserName, 
            ref int pcchMaxUserName, 
            StringBuilder pszDomainName, 
            ref int pcchMaxDomainame, 
            StringBuilder pszPassword, 
            ref int pcchMaxPassword);

        public static NetworkCredential PromptForCreds(string PromptCaption = "Credentials needed", string PromptMessage = "Please enter your username and password")
        {
            bool save = false;
            int errorcode = 0;
            uint dialogReturn;
            uint authPackage = 0;
            IntPtr outCredBuffer = IntPtr.Zero;
            uint outCredSize;

            try
            {
                CREDUI_INFO credui = new CREDUI_INFO();
                credui.cbSize = Marshal.SizeOf(credui);
                credui.pszCaptionText = PromptCaption;
                credui.pszMessageText = PromptMessage;
                IntPtr hwnd = System.Diagnostics.Process.GetCurrentProcess().MainWindowHandle;
                if (hwnd != IntPtr.Zero) credui.hwndParent = hwnd;

                int maxUserName = 256;
                int maxDomain = 100;
                int maxPassword = 127;  // Windows 10 max
                var usernameBuf = new StringBuilder(maxUserName);
                var domainBuf = new StringBuilder(maxDomain);
                var passwordBuf = new StringBuilder(maxPassword);

                while (true) //Show the dialog again and again, until Cancel is clicked or the entered credentials are correct.
                {
                    //Show the dialog
                    dialogReturn = CredUIPromptForWindowsCredentials(ref credui,
                    errorcode,
                    ref authPackage,
                    (IntPtr)0,  //You can force that a specific username is shown in the dialog. Create it with 'CredPackAuthenticationBuffer()'. Then, the buffer goes here...
                    0,          //...and the size goes here. You also have to add CREDUIWIN_IN_CRED_ONLY to the flags (last argument).
                    out outCredBuffer,
                    out outCredSize,
                    ref save,
                    0); //Use the PromptForWindowsCredentialsFlags-Enum here. You can use multiple flags if you seperate them with | .

                    if (dialogReturn != 0) break; //Break, if Cancel was clicked or an error occurred


                    /*Unpack your credentials  (outCredBuffer, outCredSize) with 'CredUnPackAuthenticationBuffer()'
                      For example, it returns a bool 'credentialsEnteredCorrect':*/
                    NetworkCredential netCredential;
                    if (CredUnPackAuthenticationBuffer(0, outCredBuffer, outCredSize, usernameBuf, ref maxUserName, domainBuf, ref maxDomain, passwordBuf, ref maxPassword))
                    {
                        //clear the memory allocated by CredUIPromptForWindowsCredentials

                        netCredential = new NetworkCredential()
                        {
                            UserName = usernameBuf.ToString(),
                            Password = passwordBuf.ToString(),
                            Domain = domainBuf.ToString()
                        };
                        return netCredential;
                    }
                }
            }
            catch (Exception e)
            {
                throw e;  // Caller needs to handle this, only here so we can release the buffer in finally
            }
            finally
            {
                if (outCredBuffer != IntPtr.Zero) CoTaskMemFree(outCredBuffer);
            }
            return null;

        }
    }
}