fix(server:socket.io): fallback for when `socket.handshake.address` is not provided

On some servers (ex. `heroku`), property `socket.handshake.address` is `null`.

This fix, adds fallback to the `DOMAIN` set in `server/config/_local.env.js`.

Also:
* eliminates need to paste `DOMAIN` for each passport Strategy, and 
* fixes bug where authenticating on `localhost` would result in an external redirect.