Is it possible to use RedirectToAction() inside a custom AuthorizeAttribute class?

You can/should override HandleUnauthorizedRequest instead of OnAuthorization. Here’s the default implementation:

    protected virtual void HandleUnauthorizedRequest(AuthorizationContext filterContext) {
        // Returns HTTP 401 - see comment in HttpUnauthorizedResult.cs.
        filterContext.Result = new HttpUnauthorizedResult();
    }

You can’t use Controller.RedirectToAction, but you can return a new RedirectToRouteResult.

So you can do:

    protected override void HandleUnauthorizedRequest(AuthorizationContext filterContext) {
        // Returns HTTP 401 - see comment in HttpUnauthorizedResult.cs.
        filterContext.Result = new RedirectToRouteResult(
                                   new RouteValueDictionary 
                                   {
                                       { "action", "ActionName" },
                                       { "controller", "ControllerName" }
                                   });
    }