Configure user's "name" via SSO

[haraldschilly]

The SSO configuration maps incoming data to database fields. This is configurable via login_info: { "emails": "email", "last_name": ..., "first_name": ... }.

What this can't do is setting the username (i.e. "accounts.name"). I.e. it should check if the name does not exist, and then set it. If it is supposed to update on login, re-set that field as well (with the same check of uniqueness). If the SSO mechanism is exclusive, block users from changing their name as well.