This is an example of how to configure nginx to allow ActionCable WebSocket connections to use the same host as your primary site.  For example, instead of `cable.myapp.dev`, you can use `myapp.dev/_c/`.

In my case, we have a multi-tenanted environment, e.g., `bob.myapp.dev` and `jim.myapp.dev`.  This lets the ActionCable connection still use the `Host:` header to select a tenant, and use normal cookies for user identification. `wss://bob.myapp.dev/_c/` is authorized as normal.  It also piggybacks off of whatever TLS setup is available.