C# – LogonUser and delegation

cdelegationimpersonationwinapi

I'm using the LogonUser win32 api:

token = LogonUser(...)
WindowsIdentity newId = new WindowsIdentity(token);            
WindowsImpersonationContext impersonatedUser = newId.Impersonate();

However when calling a WCF service after this I'm not able to use the impersonated identity. I think this is because impersonatedUser.ImpersonationLevel equals Impersonation.

Is this the reason?
Is a level of ImpersonationLevel.Identification what I need?
How to get such a level?

Best Answer

I don't know if this will work for WCF. But we use it in our production web app for impersonation to read and write files to the file system. You will need to define the API's for AdvApi32.LogonUser, AdvApi32.DuplicateToken, and Kernel32.CloseHandle and make sure to Close the WindowsImpersonationContext when you are done.

    /// <summary>impersonates a user</summary>
    /// <param name="username">domain\name of the user account</param>
    /// <param name="password">the user's password</param>
    /// <returns>the new WindowsImpersonationContext</returns>
    public static WindowsImpersonationContext ImpersonateUser(String username, String password)
    {
        WindowsIdentity winId = WindowsIdentity.GetCurrent();
        if (winId != null)
        {
            if (string.Compare(winId.Name, username, true) == 0)
            {
                return null;
            }
        }

        //define the handles
        IntPtr existingTokenHandle = IntPtr.Zero;
        IntPtr duplicateTokenHandle = IntPtr.Zero;

        String domain;
        if (username.IndexOf("\\") > 0)
        {
            //split domain and name
            String[] splitUserName = username.Split('\\');
            domain = splitUserName[0];
            username = splitUserName[1];
        }
        else
        {
            domain = String.Empty;
        }

        try
        {
            //get a security token

            bool isOkay = AdvApi32.LogonUser(username, domain, password,
                (int) AdvApi32.LogonTypes.LOGON32_LOGON_INTERACTIVE,
                (int) AdvApi32.LogonTypes.LOGON32_PROVIDER_DEFAULT,
                ref existingTokenHandle);

            if (!isOkay)
            {
                int lastWin32Error = Marshal.GetLastWin32Error();
                int lastError = Kernel32.GetLastError();

                throw new Exception("LogonUser Failed: " + lastWin32Error + " - " + lastError);
            }

            // copy the token

            isOkay = AdvApi32.DuplicateToken(existingTokenHandle,
                (int) AdvApi32.SecurityImpersonationLevel.SecurityImpersonation,
                ref duplicateTokenHandle);

            if (!isOkay)
            {
                int lastWin32Error = Marshal.GetLastWin32Error();
                int lastError = Kernel32.GetLastError();
                Kernel32.CloseHandle(existingTokenHandle);
                throw new Exception("DuplicateToken Failed: " + lastWin32Error + " - " + lastError);
            }
            // create an identity from the token

            WindowsIdentity newId = new WindowsIdentity(duplicateTokenHandle);
            WindowsImpersonationContext impersonatedUser = newId.Impersonate();

            return impersonatedUser;
        }
        finally
        {
            //free all handles
            if (existingTokenHandle != IntPtr.Zero)
            {
                Kernel32.CloseHandle(existingTokenHandle);
            }
            if (duplicateTokenHandle != IntPtr.Zero)
            {
                Kernel32.CloseHandle(duplicateTokenHandle);
            }
        }
    }
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