Demanding Permissions
How do I restrict access to an operation to particular Windows users?
There are three standard ways of doing something in WCF: through code, through attributes, and through configuration. Let's try to solve the problem using each of these methods.
Restricting access through code is done by creating a custom ServiceAuthorizationManager. Restricting access to a service operation could be done this way by looking up the service operation during the access check and comparing the caller's SID to the list of approved users. This method seems pretty clunky because it brings in a lot of service machinery unrelated to the service operation we want to secure. However, this method also seems pretty flexible because we can be very creative about how the authorization is performed if we want to go beyond simply evaluating membership.
Restricting access through attributes is done by making PrincipalPermission demands. Restricting access to a service operation could be done this way by decorating the service operation with role or user based demands. The best practice recommends using roles instead of specific users because it helps with administration, which is probably good advice for all of these approaches. Using principal permissions requires actually having the right principal for the current thread. Some extra code may end up being required anyways if the client invocation doesn't propagate the right kind of information.
Restricting access through configuration is done by setting up an external authorization provider. When in compatibility mode, there is some handy functionality provided by the ASP.NET pipeline to provide authorization integrated with ASP.NET membership providers. Even without ASP.NET though, the generic Authorization Manager can be used to manage and provide roles.
I like using the attributed-based method but that's because I don't like to type a lot of code and because I rarely need to worry about deploying services on multiple systems. Each of the methods has its own strengths and weaknesses so there isn't a universal choice that's best for everyone.
Next time: Suppressing Transactions During an Operation
