Replacing a Principal Object

Applications that provide authentication services must be able to replace the Principal object for a given thread. Furthermore, the security system must help protect the ability to replace Principal objects because a maliciously attached, incorrect Principal compromises the security of your application by claiming an untrue identity or role. Therefore, applications that require the ability to replace Principal objects must be granted the System.Security.Permissions.SecurityPermission object for principal control. (Note that this permission is not required for performing role-based security checks or for creating Principal objects.)

The current Principal object can be replaced by performing the following tasks:

1. Create the replacement Principal object and associated Identity object.

2. Attach the new Principal object to the call context.

Example

The following example shows how to create a generic principal object and use it to set the principal of a thread.

Imports System
Imports System.Threading
Imports System.Security.Permissions
Imports System.Security.Principal



Class SecurityPrincipalDemo

    ' Create a generic principal based on values from the current 
    ' WindowsIdentity. 
    Private Shared Function GetGenericPrincipal() As GenericPrincipal
        ' Use values from the current WindowsIdentity to construct 
        ' a set of GenericPrincipal roles. 
        Dim windowsIdentity As WindowsIdentity = windowsIdentity.GetCurrent()
        Dim roles(9) As String 
        If windowsIdentity.IsAuthenticated Then 
            ' Add custom NetworkUser role.
            roles(0) = "NetworkUser" 
        End If 

        If windowsIdentity.IsGuest Then 
            ' Add custom GuestUser role.
            roles(1) = "GuestUser" 
        End If 

        If windowsIdentity.IsSystem Then 
            ' Add custom SystemUser role.
            roles(2) = "SystemUser" 
        End If 

        ' Construct a GenericIdentity object based on the current Windows 
        ' identity name and authentication type. 
        Dim authenticationType As String = windowsIdentity.AuthenticationType
        Dim userName As String = windowsIdentity.Name
        Dim genericIdentity As New GenericIdentity(userName, authenticationType)

        ' Construct a GenericPrincipal object based on the generic identity 
        ' and custom roles for the user. 
        Dim genericPrincipal As New GenericPrincipal(genericIdentity, roles)

        Return genericPrincipal

    End Function 'GetGenericPrincipal

    Public Shared Sub Main()
        ' Retrieve a GenericPrincipal that is based on the current user's 
        ' WindowsIdentity. 
        Dim genericPrincipal As GenericPrincipal = GetGenericPrincipal()

        ' Retrieve the generic identity of the GenericPrincipal object. 
        Dim principalIdentity As GenericIdentity = CType(genericPrincipal.Identity, GenericIdentity)

        ' Display the identity name and authentication type. 
        If principalIdentity.IsAuthenticated Then
            Console.WriteLine(principalIdentity.Name)
            Console.WriteLine("Type:" + principalIdentity.AuthenticationType)
        End If 

        ' Verify that the generic principal has been assigned the 
        ' NetworkUser role. 
        If genericPrincipal.IsInRole("NetworkUser") Then
            Console.WriteLine("User belongs to the NetworkUser role.")
        End If

        Thread.CurrentPrincipal = genericPrincipal

    End Sub 'Main



End Class 'SecurityPrincipalDemo 

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

class SecurityPrincipalDemo
{
    public static void Main()
    {
        // Retrieve a GenericPrincipal that is based on the current user's 
        // WindowsIdentity.
        GenericPrincipal genericPrincipal = GetGenericPrincipal();

        // Retrieve the generic identity of the GenericPrincipal object.
        GenericIdentity principalIdentity =
            (GenericIdentity)genericPrincipal.Identity;

        // Display the identity name and authentication type. 
        if (principalIdentity.IsAuthenticated)
        {
            Console.WriteLine(principalIdentity.Name);
            Console.WriteLine("Type:" + principalIdentity.AuthenticationType);
        }

        // Verify that the generic principal has been assigned the 
        // NetworkUser role. 
        if (genericPrincipal.IsInRole("NetworkUser"))
        {
            Console.WriteLine("User belongs to the NetworkUser role.");
        }

        Thread.CurrentPrincipal = genericPrincipal;

    }

    // Create a generic principal based on values from the current 
    // WindowsIdentity. 
    private static GenericPrincipal GetGenericPrincipal()
    {
        // Use values from the current WindowsIdentity to construct 
        // a set of GenericPrincipal roles.
        WindowsIdentity windowsIdentity = WindowsIdentity.GetCurrent();
        string[] roles = new string[10];
        if (windowsIdentity.IsAuthenticated)
        {
            // Add custom NetworkUser role.
            roles[0] = "NetworkUser";
        }

        if (windowsIdentity.IsGuest)
        {
            // Add custom GuestUser role.
            roles[1] = "GuestUser";
        }

        if (windowsIdentity.IsSystem)
        {
            // Add custom SystemUser role.
            roles[2] = "SystemUser";
        }

        // Construct a GenericIdentity object based on the current Windows 
        // identity name and authentication type. 
        string authenticationType = windowsIdentity.AuthenticationType;
        string userName = windowsIdentity.Name;
        GenericIdentity genericIdentity =
            new GenericIdentity(userName, authenticationType);

        // Construct a GenericPrincipal object based on the generic identity 
        // and custom roles for the user.
        GenericPrincipal genericPrincipal =
            new GenericPrincipal(genericIdentity, roles);

        return genericPrincipal;
    }

}

See Also

Concepts

Principal and Identity Objects

Reference

System.Security.Permissions.SecurityPermission

Change History

Date	History	Reason
September 2008	Added an example.	Customer feedback.