AllowAnonymous not working with Custom AuthorizationAttribute

This has had me stumped for a while. None of the commonly encountered similar situations seem to apply here apparently. I've probably missed something obvious but I can't see it.

In my Mvc Web Application I use the Authorize and AllowAnonymous attributes in such a way that you have to explicitly open up an action as publicly available rather than lock down the secure areas of the site. I much prefer that approach. I cannot get the same behaviour in my WebAPI however.

I have written a custom Authorization Attribute that inherits from System.Web.Http.AuthorizeAttribute with the following:

[AttributeUsage(AttributeTargets.Class | AttributeTargets.Method, Inherited = true, AllowMultiple = true)]
public class MyAuthorizationAttribute : System.Web.Http.AuthorizeAttribute

I have this registered as a filter:

    public static void RegisterHttpFilters(HttpFilterCollection filters)
    {
        filters.Add(new MyAuthorizationAttribute());
    }

This all works as expected, actions are no longer available without credentials. The problem is that now the following method will not allow the AllowAnonymous attribute to do it's thing:

[System.Web.Http.AllowAnonymous]
public class HomeController : ApiController
{
    [GET("/"), System.Web.Http.HttpGet]
    public Link[] Index()
    {
        return new Link[] 
        { 
            new SelfLink(Request.RequestUri.AbsoluteUri, "api-root"),
            new Link(LinkRelConstants.AuthorizationEndpoint, "OAuth/Authorize/", "authenticate"),
            new Link(LinkRelConstants.AuthorizationTokenEndpoint , "OAuth/Tokens/", "auth-token-endpoint")
        };
    }
}

The most common scenario seems to be getting the two Authorize / AllowAnonymous attributes mixed up. System.Web.Mvc is for web apps and System.Web.Http is for WebAPI (as I understand it anyway).

Both of the Attributes I'm using are from the same namespace - System.Web.Http. I assumed that this would just inherit the base functionality and allow me to inject the code I need in the OnAuthotize method.

According to the documentation the AllowAnonymous attribute works inside the OnAuthorize method which I call immediately:

    public override void OnAuthorization(HttpActionContext actionContext)
    {
        base.OnAuthorization(actionContext);

Any thought's would be really appreciated.

Has anyone encountered this problem before and found the root cause?

In the AuthorizeAttribute there is the following code:

private static bool SkipAuthorization(HttpActionContext actionContext)
{
    Contract.Assert(actionContext != null);

    return actionContext.ActionDescriptor.GetCustomAttributes<AllowAnonymousAttribute>().Any()
               || actionContext.ControllerContext.ControllerDescriptor.GetCustomAttributes<AllowAnonymousAttribute>().Any();
}

Include this method in your AuthorizeAttribute class then add the following to the top of your OnAuthorization method to skip authorization if any AllowAnonymous attributes are found:

if (SkipAuthorization(actionContext)) return;

ASP.NET MVC 4:

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

or

 private static bool SkipAuthorization(AuthorizationContext filterContext)
    {
        Contract.Assert(filterContext != null);

        return filterContext.ActionDescriptor.GetCustomAttributes(typeof(AllowAnonymousAttribute), true).Any()
               || filterContext.ActionDescriptor.ControllerDescriptor.GetCustomAttributes(typeof(AllowAnonymousAttribute), true).Any();
    }

Soruce: http://weblogs.asp.net/jongalloway/asp-net-mvc-authentication-global-authentication-and-allow-anonymous

In my case, none of the above solutions worked. I am using .Net Core 3.1 with a custom IAuthorizationFilter and I had to do the following:

public void OnAuthorization(AuthorizationFilterContext context)
    {
        if (context.ActionDescriptor.EndpointMetadata.OfType<AllowAnonymousAttribute>().Any()) return;

Using MVC 5
Steps to overcome this issue:-
1. Update your Anonymous attribute of WebAPI project and make it like

[System.Web.Mvc.AllowAnonymous]

2. Now go to your custom attribute class and write the code

    public override void OnAuthorization(System.Web.Http.Controllers.HttpActionContext filterContext)
   {
       if (filterContext == null)
       {
           throw new UnauthorizedAccessException("Access Token Required");
       }
       base.OnAuthorization(filterContext);
       if (filterContext.ActionDescriptor.GetCustomAttributes<AllowAnonymousAttribute>().Any())
       {
           return;
       }
       if (filterContext.Request.Headers.Authorization != null)
       {
           var response = 
    PTPRestClient.GetRequest(filterContext.Request.Headers.Authorization.ToString(), 
    "api/validate/validate-request");
           if (!response.IsSuccessStatusCode)
           {
               throw new UnauthorizedAccessException();
           }
   
   
       }
       else
       {
           throw new UnauthorizedAccessException("Access Token Required");
       }
   }
   

Here is a solution for ASP.NET Core 2+ and ASP.NET Core 3+. Add it into IAsyncAuthorizationFilter implementation:

private static bool HasAllowAnonymous(AuthorizationFilterContext context)
{
    var filters = context.Filters;
    return filters.OfType<IAllowAnonymousFilter>().Any();
}

And check like this:

public async Task OnAuthorizationAsync(AuthorizationFilterContext context)
{
    if(HasAllowAnonymous(context))
        return;
}