Directly Accessing a Principal Object

Although using imperative and declarative demands to invoke role-based security checks is the primary mechanism for checking and enforcing identity and role membership, there might be cases where you want to access the Principal object and its associated Identity object directly to do authorization tasks without creating permission objects. For example, you might not want to use declarative or imperative demands if you do not want a thrown exception to be the default behavior for validation failure. In this case, you can use the static CurrentPrincipal property on the System.Threading.Thread class to access the Principal object and call its methods.

After obtaining the principal object, you can use conditional statements to control access to your code based on the principal name as shown in the following code example.

WindowsPrincipal MyPrincipal = (WindowsPrincipal) Thread.CurrentPrincipal;
if (MyPrincipal.Identity.Name == "fred") 
// Permit access to some code.
[Visual Basic]Dim MyPrincipal As WindowsPrincipal = _
   CType(Thread.CurrentPrincipal, WindowsPrincipal)
If (MyPrincipal.Identity.Name = "fred") Then
' Permit access to some code.
End If

You can also programmatically check role membership by calling the IsInRole method on the current Principal object as shown in the following code example.

WindowsPrincipal MyPrincipal = (Thread.CurrentPrincipal as WindowsPrincipal);
if (MyPrincipal.IsInRole("Administrator")) {
// Permit access to some code.
}
[Visual Basic]WindowsPrincipal MyPrincipal = (Thread.CurrentPrincipal as WindowsPrincipal);
If (MyPrincipal.IsInRole("Administrator")) Then
// Permit access to some code.
End If

You might use this technique when you want to access behaviors that are specific to an application-defined Principal object. However, in most cases, you use the PrincipalPermission class to control access to your code based on identity or role membership.

The following code example creates a WindowsPrincipal object and a WindowsIdentity object, sets them to the current user, and makes a security decision based on the value of the Principal. It does not use a PrincipalPermission object imperatively or declaratively, but makes an access decision based on the values of the principal object instead.

using System;
using System.Security.Permissions;
using System.Security.Policy;
using System.Security.Principal;
using System.Threading;

public class Class1
{
   public static int Main(string[] args)
   {
   //Set principal policy so that you have permission to get current user information.
          AppDomain.CurrentDomain.SetPrincipalPolicy(PrincipalPolicy.WindowsPrincipal);
   //Get the current principal and put it into a principal object.

WindowsPrincipal MyPrincipal = (Thread.CurrentPrincipal as WindowsPrincipal);

   //Check the name and see if the user is authenticated. 
            
   if(MyPrincipal.Identity.Name.Equals(@"MYDOMAIN\myuser") && MyPrincipal.Identity.IsAuthenticated.Equals(true))
   {
      Console.WriteLine("Hello {0}, you are authenticated!", MyPrincipal.Identity.Name.ToString());
   }
   else
   {
      Console.WriteLine("Go away! You are not authorized!");
   }

          return 0;
 }
}
[Visual Basic]Imports System
Imports System.Security.Permissions
Imports System.Security.Policy
Imports System.Security.Principal
Imports System.Threading

Public Class Class1

   Public Shared Sub Main()
        'Set principal policy so that you have permission to get current user information.
        AppDomain.CurrentDomain.SetPrincipalPolicy(PrincipalPolicy.WindowsPrincipal)
        'Get the current principal and put it into a principal object.
        Dim MyPrincipal As WindowsPrincipal = CType(Thread.CurrentPrincipal, WindowsPrincipal)

        'Check the name and see if the user is authenticated. 

        If (MyPrincipal.Identity.Name.Equals("MYDOMAIN\myuser") And MyPrincipal.Identity.IsAuthenticated) Then
            Console.WriteLine("Hello {0}, you are authenticated!", MyPrincipal.Identity.Name.ToString())
        Else
            Console.WriteLine("Go away! You are not authorized!")
        End If

    End Sub
End Class

If the current user is MYDOMAIN\myuser, this program displays the following message to the console.

Hello MYDOMAIN\myuser, you are authenticated!

However, if any other user is the current user, the program displays the following message.

Go away! You are not authorized!

The value in MyPrincipal.Identity.Name shows the domain and user name that represents the authorized account. Notice that in C# the string "MYDOMAIN\myuser" is prefixed with the at sign (@) so that the backslash is not interpreted as an escape character. Although the previous example uses a WindowsIdentity object, you can easily produce similar code using a generic object. Simply create an instance of the generic object, pass it the values you want, and later check the object for those values.

See Also

System.Threading.Thread.CurrentPrincipal | Role-Based Security Checks