Return Session ID when authentication is done via REST

We should receive the session_id when the authentication is successful via REST. This would allow to let an application to set the SSO cookie.

Usage example:

curl -H "Accept: application/json" -d user=rtyler -d password=rtyler http://auth.example.com:19876/
{"result":1,"id":"28c68e065248caf27870ac41b2796067800dfa7551e96aa4e671714b6c89af34","code":"0"}