Route with parameter in ASP.NET Web API using OWIN OAuthAuthorization

I'm trying to use a route like "/api/{culture}/token" for my OAuth authorization process at my Web API but I'm not succeeding on it.

 var options = new OAuthAuthorizationServerOptions()
        {
            AllowInsecureHttp = true,
            TokenEndpointPath = new PathString("/api/{culture}/token"),
            AccessTokenExpireTimeSpan = TimeSpan.FromDays(1),
            Provider = new SimpleAuthorizationServerProvider()
        };

I have seen how to access query string parameters as explained here but it would be better to call this route as, say, api/en-US/token instead of api/token/?auth_parameters&culture=en-US