Login options

This is called by the client for knowing the Oauth2 provider(s) available You must provide a list of Oauth2 providers in the oauth2.toml config file The config file can be overridden by the OAUTH2_CONFIG_FILE environment variable

Limitations

Currently it uses the client id as the user id the limitation is that the client cannot retrieve its address book if the client uses a different client. For having a real user name. We need to add a step after the Oauth2 authorization code is exchanged for an access token.