Question

I wrote a simple Windows Forms program in C#. I want to be able to input a windows user name and password and when I click a login button to run code run as the user I’ve entered as input.

Answer 1

You can use the WindowsIdentity.Impersonate method to achieve this. This method allows code to impersonate a different Windows user. Here is a link for more information on this method with a good sample:

http://msdn.microsoft.com/en-us/library/system.security.principal.windowsidentity.impersonate.aspx

Complete example:

// This sample demonstrates the use of the WindowsIdentity class to impersonate a user. // IMPORTANT NOTES: // This sample can be run only on Windows XP.  The default Windows 2000 security policy // prevents this sample from executing properly, and changing the policy to allow // proper execution presents a security risk. // This sample requests the user to enter a password on the console screen. // Because the console window does not support methods allowing the password to be masked, // it will be visible to anyone viewing the screen. // The sample is intended to be executed in a .NET Framework 1.1 environment.  To execute // this code in a 1.0 environment you will need to use a duplicate token in the call to the // WindowsIdentity constructor. See KB article Q319615 for more information.  using System; using System.Runtime.InteropServices; using System.Security.Principal; using System.Security.Permissions; using System.Windows.Forms;  [assembly:SecurityPermissionAttribute(SecurityAction.RequestMinimum, UnmanagedCode=true)] [assembly:PermissionSetAttribute(SecurityAction.RequestMinimum, Name = 'FullTrust')] public class ImpersonationDemo {     [DllImport('advapi32.dll', SetLastError=true, CharSet = CharSet.Unicode)]     public static extern bool LogonUser(String lpszUsername, String lpszDomain, String lpszPassword,         int dwLogonType, int dwLogonProvider, ref IntPtr phToken);      [DllImport('kernel32.dll', CharSet=System.Runtime.InteropServices.CharSet.Auto)]     private unsafe static extern int FormatMessage(int dwFlags, ref IntPtr lpSource,         int dwMessageId, int dwLanguageId, ref String lpBuffer, int nSize, IntPtr *Arguments);      [DllImport('kernel32.dll', CharSet=CharSet.Auto)]     public extern static bool CloseHandle(IntPtr handle);      [DllImport('advapi32.dll', CharSet=CharSet.Auto, SetLastError=true)]     public extern static bool DuplicateToken(IntPtr ExistingTokenHandle,         int SECURITY_IMPERSONATION_LEVEL, ref IntPtr DuplicateTokenHandle);      // Test harness.     // If you incorporate this code into a DLL, be sure to demand FullTrust.     [PermissionSetAttribute(SecurityAction.Demand, Name = 'FullTrust')]     public static void Main(string[] args)     {         IntPtr tokenHandle = new IntPtr(0);         IntPtr dupeTokenHandle = new IntPtr(0);         try         {             string userName, domainName;             // Get the user token for the specified user, domain, and password using the             // unmanaged LogonUser method.             // The local machine name can be used for the domain name to impersonate a user on this machine.             Console.Write('Enter the name of the domain on which to log on: ');             domainName = Console.ReadLine();              Console.Write('Enter the login of a user on {0} that you wish to impersonate: ', domainName);             userName = Console.ReadLine();              Console.Write('Enter the password for {0}: ', userName);              const int LOGON32_PROVIDER_DEFAULT = 0;             //This parameter causes LogonUser to create a primary token.             const int LOGON32_LOGON_INTERACTIVE = 2;              tokenHandle = IntPtr.Zero;              // Call LogonUser to obtain a handle to an access token.             bool returnValue = LogonUser(userName, domainName, Console.ReadLine(),                 LOGON32_LOGON_INTERACTIVE, LOGON32_PROVIDER_DEFAULT,                 ref tokenHandle);              Console.WriteLine('LogonUser called.');              if (false == returnValue)             {                 int ret = Marshal.GetLastWin32Error();                 Console.WriteLine('LogonUser failed with error code : {0}', ret);                 throw new System.ComponentModel.Win32Exception(ret);             }              Console.WriteLine('Did LogonUser Succeed? ' + (returnValue? 'Yes' : 'No'));             Console.WriteLine('Value of Windows NT token: ' + tokenHandle);              // Check the identity.             Console.WriteLine('Before impersonation: '                 + WindowsIdentity.GetCurrent().Name);             // Use the token handle returned by LogonUser.             WindowsIdentity newId = new WindowsIdentity(tokenHandle);             WindowsImpersonationContext impersonatedUser = newId.Impersonate();              // Check the identity.             Console.WriteLine('After impersonation: '                 + WindowsIdentity.GetCurrent().Name);              // Stop impersonating the user.             impersonatedUser.Undo();              // Check the identity.             Console.WriteLine('After Undo: ' + WindowsIdentity.GetCurrent().Name);              // Free the tokens.             if (tokenHandle != IntPtr.Zero)                 CloseHandle(tokenHandle);          }         catch(Exception ex)         {             Console.WriteLine('Exception occurred. ' + ex.Message);         }      } }