Determine if current page requires authorization?

Question

So, I have web apps with web.configs like so:

<authorization>
  <deny users="?"/>
</authorization>
...
<location path="SomeUnsecuredPage.aspx">
  <system.web>
    <authorization>
      <allow users="*"/>
    </authorization>
  </system.web>
</location>

In other words, most pages require authentication and authorization, but some don't.

Then I have an IHttpModule that will be used by all the different applications. All I want to do is check if the current request is "secured" at all. If the page doesn't require authorization I don't want my IHttpModule to do anything at all. I am using FormsAuthentication and I assume that FormsAuthentication already has all of this information cached somewhere, doesn't it? Also, since this check will be running constantly so it has to be very quick.

I am currently subscribing to the HttpApplication.AuthorizeRequest, but surprisingly this event fires even for resources that allow anonymous access.

Any ideas? Thanks for reading!

Answer 1

I think if server returns response with 401 Unauthorized status code, resource may require authorization. But sometimes server may redirect to login page, so this method is not very reliable.

Answer 2

derp!

HttpContext.Current.SkipAuthorization

Answer 3

Create a bootleg IPrincipal and then you have to use that. If the bootleg principal has access then anonymous access is allowed.

public static class AnonymousAccessCheck
            {
                public static bool IsAnonymousAccessAllowed(HttpRequest request)
                {
                    // unfortunately checking if a page allows anonymous access is more complicated than you'd think(I think).
                    // here we have to create a "Fake" IPrincipal that will only ever have access to 
                    // pages that allow anonymous access.  That way if our fake principal has access,
                    // then anonymous access is allowed

                    UrlAuthorizationModule urlAuthorizationModule = new UrlAuthorizationModule();
                    return UrlAuthorizationModule.CheckUrlAccessForPrincipal(request.Path, AnonymousPrincipal.Instance, request.RequestType);
                }

                private class AnonymousPrincipal : IPrincipal
                {
                    private static AnonymousPrincipal _Instance;
                    public static AnonymousPrincipal Instance
                    {
                        get
                        {
                            if (_Instance == null)
                                _Instance = new AnonymousPrincipal();

                            return _Instance; 
                        }
                    }

                    private AnonymousPrincipal()
                    {
                        _Identity = new AnonymousIdentity();
                    }

                    private readonly IIdentity _Identity;

                    #region IPrincipal Members

                    public IIdentity Identity
                    {
                        get { return _Identity; }
                    }

                    public bool IsInRole(string role)
                    {
                        return false;
                    }

                    #endregion

                    private class AnonymousIdentity : IIdentity
                    {
                        #region IIdentity Members
                        public string AuthenticationType
                        {
                            get { return string.Empty; }
                        }

                        public bool IsAuthenticated
                        {
                            get { return false; }
                        }

                        public string Name
                        {
                            get { return string.Empty; }
                        }
                        #endregion
                    }
                }
            }