Open a shared file under another user and domain?

Question

I have a C# console application that needs to read a shared file on a machine in another domain. When the application tries to access the file an exception occurs as the local user does not have permission to access the shared resource.

Currently I overcome this problem manually by open the shared folder from the run and put the username and password into the windows authentication dialog then run the application.

How can I do it programmatically?

Answer 1

I used the point "a" as Anton suggested, I developed two versions for one class, the first one using the Win32 APIs, and the second uses the WindowsIdentity class.

Version 1:

class UserImpersonation : IDisposable
{       
    [DllImport("advapi32.dll")]
    public static extern int LogonUser(String lpszUserName,
        String lpszDomain,
        String lpszPassword,
        int dwLogonType,
        int dwLogonProvider,
        ref IntPtr phToken);

    [DllImport("advapi32.dll", CharSet = CharSet.Auto, SetLastError = true)]
    public static extern int DuplicateToken(IntPtr hToken,
        int impersonationLevel,
        ref IntPtr hNewToken);

    [DllImport("advapi32.dll", CharSet = CharSet.Auto, SetLastError = true)]
    public static extern bool RevertToSelf();

    [DllImport("kernel32.dll", CharSet = CharSet.Auto)]
    public static extern bool CloseHandle(IntPtr handle);

    const int LOGON32_PROVIDER_DEFAULT = 0;
    const int LOGON32_LOGON_INTERACTIVE = 2;

    WindowsImpersonationContext wic;
    string _userName;
    string _domain;
    string _passWord;
    
    public UserImpersonation(string userName, string domain, string passWord)
    {
        _userName = userName;
        _domain = domain;
        _passWord = passWord;
    }
    
    public bool ImpersonateValidUser()
    {
        WindowsIdentity wi;
        IntPtr token = IntPtr.Zero;
        IntPtr tokenDuplicate = IntPtr.Zero;

        if (RevertToSelf())
        {
            if (LogonUser(_userName, _domain, _passWord, LOGON32_LOGON_INTERACTIVE,
                LOGON32_PROVIDER_DEFAULT, ref token) != 0)
            {
                if (DuplicateToken(token, 2, ref tokenDuplicate) != 0)
                {
                    wi = new WindowsIdentity(tokenDuplicate);
                    wic = wi.Impersonate();
                    if (wic != null)
                    {
                        CloseHandle(token);
                        CloseHandle(tokenDuplicate);
                        return true;
                    }
                }
            }
        }
        
        if (token != IntPtr.Zero)
        {
            CloseHandle(token);
        }
        if (tokenDuplicate != IntPtr.Zero)
        {
            CloseHandle(tokenDuplicate);
        }
        return false;
    }

    #region IDisposable Members
    public void Dispose()
    {
        if (wic != null)
        {
            wic.Dispose();
        }
        RevertToSelf();
    }
    #endregion
}

Version2 (from MSDN with small changes):

class UserImpersonation2 : IDisposable
{
    [DllImport("advapi32.dll")]
    public static extern bool LogonUser(String lpszUserName,
        String lpszDomain,
        String lpszPassword,
        int dwLogonType,
        int dwLogonProvider,
        ref IntPtr phToken);

    [DllImport("kernel32.dll", CharSet = CharSet.Auto)]
    public static extern bool CloseHandle(IntPtr handle);

    WindowsImpersonationContext wic;
    IntPtr tokenHandle;
    string _userName;
    string _domain;
    string _passWord;

    public UserImpersonation2(string userName, string domain, string passWord)
    {
        _userName = userName;
        _domain = domain;
        _passWord = passWord;
    }

    const int LOGON32_PROVIDER_DEFAULT = 0;
    const int LOGON32_LOGON_INTERACTIVE = 2;

    public bool ImpersonateValidUser()
    {
        bool returnValue = LogonUser(_userName, _domain, _passWord,
                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);
            return false;
        }

        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);
        wic = newId.Impersonate();

        // Check the identity.
        Console.WriteLine("After impersonation: "
            + WindowsIdentity.GetCurrent().Name);
            
        return true;
    }
    
    #region IDisposable Members
    public void Dispose()
    {
        if(wic!=null)
        {
            wic.Undo();
        }
        if (tokenHandle != IntPtr.Zero)
        {
            CloseHandle(tokenHandle);
        }
    }
    #endregion
}

How to use (both are the same):

const string file = @"\\machine\test\file.txt";

using (UserImpersonation user = new UserImpersonation("user", "domain", "password"))
{
    if (user.ImpersonateValidUser())
    {
        StreamReader reader = new StreamReader(file);
        Console.WriteLine(reader.ReadToEnd());
        reader.Close();
    }
}

Answer 2

a) p/invoke LogonUser with LOGON32_LOGON_NEW_CREDENTIALS and create a new WindowsIdentity with the new token, then use normal file access.

b) p/invoke WNetAddConnection3. Be advised that this makes your remote share accessible to every other process on your machine.

c) WMI via System.Management and CIM_DataFile; you won't even need p/invoke. System.Management lets you specify credentials for remote machine.

Answer 3

From memory you'll need to use a Windows API call and login as a user on the other domain. See this link for an example.

Another idea could be to use the RunAs command line argument to read the file and save it into a file on your local domain/server.