Ready to create a new branch for the download of the new user auth'ed
certificate.

Next step in this branch: detect what the selected provider support in
terms of authenticated/anon users, and show login/logout methods
consecuently.
After loggin in successfully, the new client certificate is downloaded.

It is stored in SharedPrefs, with ConfigHelper.cert_key (="cert") key.
Log in and Log out options are shown only if allow registration is true.

Allow registration is present in provider.json.

Provider.json is downloaded from both preseeded and custom providers.

Authentication success or fail is notified correctly to the user.