Specify Domain in Owin Startup Class

Question

I've created a self hosting Owin/SignalR app with code similar to the code in this tutorial:

SignalR Self Host Tutorial

Everything works, but for security-sake, I'd like to limit it to only allow messages from a specific remote site. In other words, I'd like to replace the "app.UseCors(CorsOptions.AllowAll);" line with code to confine the app to only responding to messages from a URL that I define, i.e. only allow messages from, say, http://www.remote_site.com or something. Is there any easy way to do this?

For reference, here is the code for my SignalR startup class:

using System;
using Microsoft.AspNet.SignalR;
using Microsoft.Owin.Hosting;
using Owin;
using Microsoft.Owin.Cors;

namespace SignalRSelfHost
{
    public class Startup
    {
        public void Configuration(IAppBuilder app)
        {
            app.UseCors(CorsOptions.AllowAll);
            app.MapSignalR();

        // How do I only allow a specific URL instead of the "CorsOptions.AllowAll" option?             
        }
    }
}

Answer 1

Here is the full implementation of the Owin Startup class:

using System.Threading.Tasks;
using Microsoft.Owin;
using Owin;
using Microsoft.Owin.Cors;
using System.Web.Cors;

[assembly: OwinStartup(typeof(SignalRSelfHost.Startup))]

namespace SignalRSelfHost
{
    public class Startup
    {

        public void Configuration(IAppBuilder app)
        {
            var policy = new CorsPolicy()
            {
                AllowAnyHeader = true,
                AllowAnyMethod = true,
                SupportsCredentials = true
            };

            policy.Origins.Add("domain"); //be sure to include the port:
//example: "http://localhost:8081"

            app.UseCors(new CorsOptions
            {
                PolicyProvider = new CorsPolicyProvider
                {
                    PolicyResolver = context => Task.FromResult(policy)
                }
            });

            app.MapSignalR();
        }
    }
}

Also, if you want to server to accept a list of domains, you simply add them to the Origins.

Hope this helps! Good luck!

Answer 2

Here's the code that I mentioned in a comment above:

public class Startup
{

    public void Configuration(IAppBuilder app)
    {
        app.UseCors(_corsOptions.Value);
        app.MapSignalR(); 
    }


    private static Lazy<CorsOptions> _corsOptions = new Lazy<CorsOptions>(() =>
    {
        return new CorsOptions
        {
            PolicyProvider = new CorsPolicyProvider
            {
                PolicyResolver = context =>
                {
                    var policy = new CorsPolicy();
                    policy.Origins.Add("http://localhost:8081");
                    policy.AllowAnyMethod = true;
                    policy.AllowAnyHeader = true;
                    policy.SupportsCredentials = true;
                    return Task.FromResult(policy);
                }
            }
        };
    });

}

This works, but I think Matei's answer above is cleaner and simpler.