Respond with 403 if Authorization header is not present

:koala: :bug: 

This PR fixes an issue where the API would return 200 with an empty response body if there was no Authorization header in the request. This is causing the Setup guide to fail silently for some users.

/cc @jwswj @maximeprades @ebizmarts
@danielbreves ok so Customer get back to me and told that he is not using that ELSE.
So I'll remove this and leave the IF as it was in the first place.