SignalR CORS on Azure Mobile Services Web Api

I have an Azure Mobile Service running Web Api and c# and enabled CORS as suggested in Enable CORS on Azure Mobile Serivce .NET Backend
however I have now come to add SignalR into the mix.

SignalR is working fine however I can’t see to find how to enable CORS.

At present in my test app config I have the following:

//enable CORS for WebAPI
var cors = new EnableCorsAttribute("*", "*", "*");
httpconfig.EnableCors(cors);
//rather than use the static method new up SignalRExtensionConfig and pass the current config, hopefully allowing CORS...
var signalRConfig = new SignalRExtensionConfig();
signalRConfig.Initialize(httpconfig, ioc);

But CORS doesn’t work for SignalR hubs, it only works for WebAPI 🙁 I get the frustrating:

No ‘Access-Control-Allow-Origin’ header is present on the requested
resource. Origin ‘null’ is therefore not allowed access.

I have inspected the response headers and can confirm nothing is being sent back.

Can anyone advise?

Answers:

Thank you for visiting the Q&A section on Magenaut. Please note that all the answers may not help you solve the issue immediately. So please treat them as advisements. If you found the post helpful (or not), leave a comment & I’ll get back to you as soon as possible.

Method 1

I’m using the code below to add CORS to SignalR in my WebAPI project. But it’s not running inside Mobile Service. Not sure if this helps.

    public class Startup
    {
        public void Configuration(IAppBuilder app)
        {
            app.Map("/signalr", map =>
                {
                    // Setup the CORS middleware to run before SignalR.
                    // By default this will allow all origins. You can 
                    // configure the set of origins and/or http verbs by
                    // providing a cors options with a different policy.
                    map.UseCors(CorsOptions.AllowAll);
                    var hubConfiguration = new HubConfiguration
                    {
                        // You can enable JSONP by uncommenting line below.
                        // JSONP requests are insecure but some older browsers (and some
                        // versions of IE) require JSONP to work cross domain
                        // EnableJSONP = true
                        EnableJavaScriptProxies = false
                    };
                    // Run the SignalR pipeline. We're not using MapSignalR
                    // since this branch already runs under the "/signalr" path.
                    map.RunSignalR(hubConfiguration);
                });
        }
    }

Pasted as an answer since it doesn’t multi-line codes in comment. Please ignore if it doesn’t help.

Method 2

I have found a way to enable CORS for SignalR but it doesn’t seem the “Correct” way. But it’s enough to get playing with for development until I hear back from our Mobile Services friends.

The Azure Mobile Services SignalR NuGet package contains a OwinAppBuilderExtension class. This class is used during startup to extend the Owin setup for signalr. I then subclassed this and overrode the ConfigureSignalR method.

Inside this method you get access to IAppBuilder. Once here I simply added appBuilder.UseCors(CorsOptions.AllowAll); before base.ConfigureSignalR(appBuilder);

Now this is far from ideal as I have enabled CORS for everything and said to allow all. But for dev testing this is OK and I will provide a custom CORS Policy later any how.

The final step is to set our new subcclass(CORSSignalROwinAppBuilderExtension) to be used by our service.

Within your HttpConfig setup

 var configBuilder = new ConfigBuilder(options, (httpconfig, ioc) =>
 {
       ioc.RegisterInstance(new CORSSignalROwinAppBuilderExtension(httpconfig)).As<IOwinAppBuilderExtension>();
 });

Hope this helps

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0