Custom AuthorizeAttribute with custom authentication

Question

I am using ASP.NET MVC 4 Web application as a front-end for some WCF services. All the user log in/log out and session control is done on the back-end. MVC app should only

Answer 1

Here is how I did it for now:

  public class MyAuthorizeAttribute : AuthorizeAttribute
    {
        public override void OnAuthorization(AuthorizationContext filterContext)
        {
            bool authorized = false;

            /// MVC 4 boilerplate code follows
            if (filterContext == null)
                throw new ArgumentNullException("filterContext");

            bool skipAuthorization = filterContext.ActionDescriptor.IsDefined(typeof(AllowAnonymousAttribute), inherit: true)
                          || filterContext.ActionDescriptor.ControllerDescriptor.IsDefined(typeof(AllowAnonymousAttribute), inherit: true);

            if (skipAuthorization)
            {
                return;
            }

            if (OutputCacheAttribute.IsChildActionCacheActive(filterContext))
            {
                throw new InvalidOperationException(
                    "MyAuthorizeAttribute cannot be used within a child action caching block."
                );
            }
            // end of MVC code


            // custom code
            if (!AuthorizeCore(filterContext.HttpContext))
            {
                // if not authorized from some other Action call, let's try extracting user data from custom encrypted cookie
                var identity = MyEncryptedCookieHelper.GetFrontendIdentity(filterContext.HttpContext.Request);
                // identity might be null if cookie not received
                if (identity == null)
                {
                    filterContext.HttpContext.User = new GenericPrincipal(new GenericIdentity(""), null);
                }
                else
                {
                    authorized = true;
                    filterContext.HttpContext.User = new MyFrontendPrincipal(identity);
                }

                // make sure the Principal's are in sync - there might be situations when they are not!
                Thread.CurrentPrincipal = filterContext.HttpContext.User;
            }

            // MVC 4 boilerplate code follows
            if (authorized)
            {
                // ** IMPORTANT **
                // Since we're performing authorization at the action level, the authorization code runs
                // after the output caching module. In the worst case this could allow an authorized user
                // to cause the page to be cached, then an unauthorized user would later be served the
                // cached page. We work around this by telling proxies not to cache the sensitive page,
                // then we hook our custom authorization code into the caching mechanism so that we have
                // the final say on whether a page should be served from the cache.

                HttpCachePolicyBase cachePolicy = filterContext.HttpContext.Response.Cache;
                cachePolicy.SetProxyMaxAge(new TimeSpan(0));
                cachePolicy.AddValidationCallback(CacheValidateHandler, null /* data */);
            }
            else
            {
                HandleUnauthorizedRequest(filterContext);
            }
            //end of MVC code
        }

        protected override bool AuthorizeCore(HttpContextBase httpContext)
        {
            if (httpContext == null)
                throw new ArgumentNullException("httpContext");

            // check to make sure the user is authenticated as my custom identity
            var principal = httpContext.User as MyFrontendPrincipal;
            if (principal == null)
                return false;

            var identity = principal.Identity as MyFrontendIdentity;
            if (identity == null)
                return false;

            return true;
        }

        protected override void HandleUnauthorizedRequest(AuthorizationContext filterContext)
        {            
            // default MVC result was:
            // filterContext.Result = new HttpUnauthorizedResult();

            // but I redirect to index login page instead of kicking 401
            filterContext.Result = new RedirectResult("/Home/Index/NeedsLogin");
        }

        // MVC 4 boilerplate code follows
        private void CacheValidateHandler(HttpContext context, object data, ref HttpValidationStatus validationStatus)
        {
            validationStatus = OnCacheAuthorization(new HttpContextWrapper(context));
        }

        // This method must be thread-safe since it is called by the caching module.
        protected virtual HttpValidationStatus OnCacheAuthorization(HttpContextBase httpContext)
        {
            if (httpContext == null)
                throw new ArgumentNullException("httpContext");

            bool isAuthorized = AuthorizeCore(httpContext);
            return (isAuthorized) ? HttpValidationStatus.Valid : HttpValidationStatus.IgnoreThisRequest;
        }
    } 

It does not handle my 3rd scenario, though, so I'll implement it in a global error handler.

Answer 2

Regarding your first requirement:

As you already found out, OnAuthorization takes care of a number of aspects, including e.g. caching.
If you are only interested in customizing the way in which user credentials are validated, I suggest you go for overriding AuthorizeCore instead. E.g.:

public class ClientCookieAuthorizeAttribute : AuthorizeAttribute
{
    protected override bool AuthorizeCore(HttpContextBase httpContext)
    {
        HttpCookie cookie = httpContext.Request.Cookies[_tokenCookieName];

        bool isAuthenticated = ValidateUserByCookie(cookie);

        return isAuthenticated;
    }

    private bool ValidateUserByCookie(HttpCookie cookie)
    {
        var result = false;
        // Perform validation
        // You could include httpContext as well, to check further information
        return result;
    }

    private static const string _tokenCookieName = "myCookieName";
}

You might also want to give a look at this other threads:

1. SO - Custom Authorize Attribute
2. ASP.NET - Custom AuthorizationFilter redirect problems
3. Diary of a ninja

Answer 3

Not totally sure I get it but if you create an Custom Authorization Filter that inherits from System.Web.MVC.Authorize attribute like this.

    public class CustomAuthorize : AuthorizeAttribute
    {
    public override void OnAuthorization(AuthorizationContext filterContext)
    {
        if (CookieIsValid(filterContext.Request.Cookies["cookieyouwant"])
        {
             filterContext.Result = new RedirectResult("DestUrl");
        }
        else
        {
            filterContext.Result = new RedirectResult("/Home/Index/NeedsLogin");
        }
    }
}

And then decorate your Methods that need to employ this Authorization will that do the trick?