how to tell if my asp.net mvc application is accessed via a proxy?

Question

I would like to serve another content depending on whether a user is using a proxy server or not.

        if(FROM_PROXY){
          routes.MapRoute(
            name: "ProxyDefault",
            url: "{controller}/{action}/{id}",
            defaults: new { controller = "HomeProxy",
              action = "Index", id = UrlParameter.Optional 
            }
          );
        }

So, how to detect if my asp.net mvc application is accessed via a proxy?

Some proxies are transparent so there's no way to be 100% sure. — DavidG, Feb 05 '15 at 11:42
Routes registration are performed once at application startup, at this stage no HTTP request is present and no way to determine proxy. — haim770, Feb 05 '15 at 11:43
Why do you want to route proxied users to another controller? Do you need different behavior? Different view? — haim770, Feb 05 '15 at 11:46
@haim770 thank you but It's just an example! What I really need is to detect if user is on a proxy, so I can prevent the user... — Bellash, Feb 05 '15 at 11:56
By "preventing the user" you mean that you want to return an "401 Unauthorized" response? Or redirect the user to another error page? — haim770, Feb 05 '15 at 12:18

score 0 · Accepted Answer · edited May 23 '17 at 10:26

You can register the following global filter:

[AttributeUsage(AttributeTargets.Class | AttributeTargets.Method)]
public class BlockProxyAccessAttribute : ActionFilterAttribute
{
    private static readonly string[] HEADER_KEYS = { "VIA", "FORWARDED", "X-FORWARDED-FOR", "CLIENT-IP" };
    private const string PROXY_REDIR_URL = "/error/proxy";

    public override void OnActionExecuting(ActionExecutingContext filterContext)
    {
        var isProxy = filterContext.HttpContext.Request.Headers.AllKeys.Any(x => HEADER_KEYS.Contains(x));

        if (isProxy)
            filterContext.Result = new RedirectResult(PROXY_REDIR_URL);
    }
}

(The candidate header keys for proxy determination are taken from this answer)

Thanks! It helped for some proxies. – Bellash Feb 05 '15 at 14:52 — Bellash, Feb 05 '15 at 14:52

how to tell if my asp.net mvc application is accessed via a proxy?

1 Answers1