Custom Authorization in Asp.net WebApi - what a mess?
asp.net, asp.net-web-api, authorization
Solution
Which methods should I use : IsAuthorized or OnAuthorization ? ( or when to use which)
You will extend `AuthorizationFilterAttribute` if your authorization logic is not dependent on the identity established and roles. For user related authorization, you will extend and use `AuthorizeAttribute`. For the former case, you will override `OnAuthorization`. For the latter case, you will override `IsAuthorized`. As you could see from the source code of these attributes, `OnAuthorization` is marked virtual for you to override if you derive from `AuthorizationFilterAttribute`. On the other hand, the `IsAuthorized` method is marked virtual in `AuthorizeAttribute`. I believe this is a good pointer to the intended usage.
when should I call base.IsAuthorized or base.OnAuthorization?
The answer to this question lies in how OO generally works. If you override a method, you can either completely provide a new implementation or piggy back on the implementation provided by parent and enhance the behavior. For example, take the case of `IsAuthorized(HttpActionContext)`. The base class behavior is to check the user/role against what is specified in the filter vs the identity established. Say, you want to do all that but in addition, you want to check something else, may be based on a request header or something. In that case, you can provide an override like this.
protected override bool IsAuthorized(HttpActionContext actionContext)
{
bool isAuthroized = base.IsAuthorized(actionContext);
// Here you look at the header and do your additional stuff based on actionContext
// and store the result in isRequestHeaderOk
// Then, you can combine the results
// return isAuthorized && isRequestHeaderOk;
}
I'm sorry but don't understand your Q3. BTW, Authorization filter has been around for a long time and people use it for all kinds of things and sometimes incorrectly as well.
One more thing. And finally there was this guy here who said : You shouldn't override OnAuthorization - because you would be missing [AllowAnonymous] handling.
The guy who said that is the God of access control - Dominick. Obviously it will be correct. If you look at the implementation of `OnAuthorization` (copied below),
public override void OnAuthorization(HttpActionContext actionContext)
{
if (actionContext == null)
{
throw Error.ArgumentNull("actionContext");
}
if (SkipAuthorization(actionContext))
{
return;
}
if (!IsAuthorized(actionContext))
{
HandleUnauthorizedRequest(actionContext);
}
}
the call to `SkipAuthorization` is the part that ensures `AllowAnonymous` filters are applied, that is, authorization is skipped. If you override this method, you loose that behavior. Actually, if you decide to base your authorization on users/roles, at that point you would have decided to derive from `AuthorizeAttribute`. Only correct option left for you at that point will be to override `IsAuthorized` and not the already overridden `OnAuthorization`, although it is technically possible to do either.
PS. In ASP.NET Web API, there is another filter called authentication filter. Idea is that you use that for authentication and authorization filter for authorization, as the name indicates. However, there are lots of examples where this boundary is fudged. Lots of authroization filter examples will do some kind of authentication. Anyways, if you have time and want to understand a bit more, take a look at this MSDN article. Disclaimer: It was written by me.
Problem
I'm reading from several resources (books and SO answers) about authorization in WebApi. Suppose I want to add Custom Attribute which allows access only for Certain Users: Case #1 I've seen this approach of overriding `OnAuthorization` , which sets response if something is wrong ``` public class AllowOnlyCertainUsers : AuthorizeAttribute { public override void OnAuthorization(HttpActionContext actionContext) { if ( /*check if user OK or not*/) { actionContext.Response = new HttpResponseMessage(HttpStatusCode.Unauthorized); } } } ``` Case #2 But I've also seen this similar example which also overriding `OnAuthorization` but with calling to `base` : ``` public override void OnAuthorization(HttpActionContext actionContext) { base.OnAuthorization(actionContext); // If not authorized at all, don't bother if (actionContext.Response == null) { //... } } ``` Then, you check if the `HttpActionContext.Response` is set or not. If it’s not set, it means that the request is authorized and the user is ok Case #3 But I've also seen this approach of overriding `IsAuthorized` : ``` public class AllowOnlyCertainUsers : AuthorizeAttribute { protected override bool IsAuthorized(HttpActionContext context) { if ( /*check if user OK or not*/) { return true;// or false } } } ``` Case #4 And then I saw similar example one but with calling base.IsAuthorized(context) : ``` protected override bool IsAuthorized(HttpActionContext context) { if (something1 && something2 && base.IsAuthorized(context)) //?? return true; return false; } ``` One more thing And finally Dominick said here : You shouldn't override OnAuthorization - because you would be missing [AllowAnonymous] handling. Questions 1) Which methods should I use : `IsAuthorized` or `OnAuthorization` ? ( or when to use which) 2) when should I call `base.IsAuthorized or` base.OnAuthorization` ? 3) Is this how they built it ? that if the response is null then everything is ok ? ( case #2) NB Please notice , I'm using ( and want to use ) only `AuthorizeAttribute` which already inherits from `AuthorizationFilterAttribute` Why ? Becuase I'm at the first stage in : http://www.asp.net/web-api/overview/security/authentication-and-authorization-in-aspnet-web-api Anyway Im asking via extending Authorize attribute .