how to integrate asp.net mvc page containing signalR with other platforms

It's difficult to pin down exactly what you need to do, cause the question is rather broad, but I hope that these points help(ed) somewhat:

SignalR cross-domain uses JavaScript on the client side and CORS on the server side, so you're covered on that front. You could easily create a JavaScript file that can connect into the SignalR channel without any changes to PHP code other than to include the JavaScript in the client's page.

You could quite easily create a single script on your server that the client can reference on their page that pulls everything required on to the client's page. Because the script executes from your own server I don't think you'll need to worry about CORS cause it's not truly 'cross site scripting', because the code executing the requests will be 'owned' by your server/domain.

As for authentication, if it's only your script that needs access to the authentication, I think that means that you can make use of your domain's authentication too (cookies etc.) I'd have to check up on that one though. Ultimately you'd authenticate them using a HTTPs request to your domain from the included script?

Here are some useful threads that might help with that one:

• Cross-Domain Cookies
• Creating a javascript cookie on a domain and reading it across sub domains