facebook app with multiple subdomains

I had a requirement of adding facebook integration with our Rails app. I am using omniauth-facebook gem for the authentication part and it works great.

Our app has multiple subdomains for all clients, so i wanted to callback URLs separate for each client.

For example,

For foo.example.com, callback should be http://foo.example.com/auth/facebook For bar.example.com, callback should be http://bar.example.com/auth/facebook

We can do that in our Facebook app settings, using App Domains field.

The description of App Domains is as follows:

Enable auth on domain and subdomain(s) (e.g., “example.com” will enable *.example.com)

To test this locally, i added entries in /etc/hosts/ for testing

    127.0.0.1   foo.myapp.com
    127.0.0.1   bar.myapp.com
    127.0.0.1   baz.myapp.com

Then accessing foo.myapp.com:3000 and bar.myapp.com:3000 and clicking on facebook authenticaton, it redirected me correctly to foo.myapp.com:3000/auth/facebook and bar.myapp.com:3000/auth/facebook respectively.

In production, we have to replace the App Domain with actual URL of our website.