Remove non-working Facebook authentication

Author: roderickvd

docs/authentication.md

@@ -57,20 +57,4 @@ login_data = AES192-DECRYPT(key, data)
 ```
 
 ## Facebook based Authentication
-The client starts an HTTPS server, and makes the user visit
-`https://login.spotify.com/login-facebook-sso/?csrf=CSRF&port=PORT`
-in their browser, where CSRF is a random token, and PORT is the HTTPS server's port.
-
-This will redirect to Facebook, where the user must login and authorize Spotify, and
-finally make a GET request to
-`https://login.spotilocal.com:PORT/login/facebook_login_sso.json?csrf=CSRF&access_token=TOKEN`,
-where PORT and CSRF are the same as sent earlier, and TOKEN is the facebook authentication token.
-
-Since `login.spotilocal.com` resolves the 127.0.0.1, the request is received by the client.
-
-The client must then contact Facebook's API at
-`https://graph.facebook.com/me?fields=id&access_token=TOKEN`
-in order to retrieve the user's Facebook ID.
-
-The Facebook ID is the `username`, the TOKEN the `auth_data`, and `auth_type` is set to `AUTHENTICATION_FACEBOOK_TOKEN`.
-
+Facebook authentication is currently broken due to Spotify changing the authentication flow. The details of how the new flow works are detailed in https://github.com/librespot-org/librespot/issues/244 and will be implemented at some point in the future.