WindowsIdentity Impersonation

public class ImpersonateUser
{
    [DllImport("advapi32.dll", SetLastError = true)]
    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 extern static bool CloseHandle(IntPtr handle);
    private static IntPtr tokenHandle = new IntPtr(0);
    private static WindowsImpersonationContext impersonatedUser;
    // If you incorporate this code into a DLL, be sure to demand that it
    // runs with FullTrust.
    [PermissionSetAttribute(SecurityAction.Demand, Name = "FullTrust")]
    public void Impersonate(string domainName, string userName, string password)
    {
        //try
        {
            // Use the unmanaged LogonUser function to get the user token for
            // the specified user, domain, and password.
            const int LOGON32_PROVIDER_DEFAULT = 0;
            // Passing this parameter causes LogonUser to create a primary token.
            const int LOGON32_LOGON_INTERACTIVE = 2;
            tokenHandle = IntPtr.Zero;
            // ---- Шаг- 1
            // Call LogonUser to obtain a handle to an access token.
            bool returnValue = LogonUser(
            userName,
            domainName,
            password,
            LOGON32_LOGON_INTERACTIVE,
            LOGON32_PROVIDER_DEFAULT,
            ref tokenHandle); // tokenHandle - new security token
            if (false == returnValue)
            {
                int ret = Marshal.GetLastWin32Error();
                throw new System.ComponentModel.Win32Exception(ret);
            }
            // ---- Шаг- 2
            WindowsIdentity newId = new WindowsIdentity(tokenHandle);
            // ---- Шаг- 3
            impersonatedUser = newId.Impersonate();
        }
    }
    // Stops impersonation
    public void Undo()
    {
        impersonatedUser.Undo();
        // Free the tokens.
        if (tokenHandle != IntPtr.Zero)
            CloseHandle(tokenHandle);
    }
}

Пример использования класса:

private void button2_Click(object sender, System.EventArgs e)
{         
    ImpersonateUser iu = new ImpersonateUser();
    iu.Impersonate("testdomen", "testuser", "testpassword");
    //Здесь размещаете код который необходимо выполнить от учетной записи
    MessageBox.Show("Test");
    iu.Undo();
}

Дополнительную информацию можете посмотреть тут.