.NET provides alternative way to enforce role and user rules. Instead of approach described in the article How to use IsInRole method to check authorization in ASP.NET in C#, you can use the PrincipalPermission class from the System.Security.Permissions namespace. You should follow the next steps:

1. Create a PrincipalPermission object that represents the user or role information you require

2. Invoke the PrincipalPermission.Demand() method.

3. If the current user doesn’t meet the requirements, a SecurityException will be thrown, which you can catch or deal with using a custom error page.

 

The constructor of the PrincipalPermission provides four overloads, from one up to three parameters, which are in turn evaluated by the Demand() method of the class:

– User name

– Role name

– Flag that asks the PrincipalPermission’s Demand() method to verify if the user is authenticated or not (isAuthenticated).

– PermissionState parameter which is inherited by the base class of the PrincipalPermission class

Note: You can omit either one of these parameters by supplying a null reference in its placeFor example with the following code you can test whether the user is a Windows administrator: 
try{

PrincipalPermission pp = new PrincipalPermission(null,@”BUILTIN\Administrators”);

pp.Demand();

// If the code reaches this point, the demand succeeded.

// The current user is an administrator.

}catch (SecurityException err){

// The demand failed. The current user isn’t an administrator.

}
 Advantage of this approach:

You don’t need need to write any conditional logic, because you can only demand all the permissions you need. This works well when you need to verify that a user is a member of multiple groups

Disadvantage of this approach: By using exception handling to control the flow of your application is slower. 

Often, PrincipalPermission checks are used in addition to web.config rules as a failsafe. You can call Demand() to ensure that even if a web.config file has been inadvertently modified, users in the wrong groups won’t be allowed