Store username provided by auth service when possible, instead of user input

Checked for duplicates

Yes - I've already checked

Is this a regression?

No - This is a new bug

Version

2.7.0

Describe the bug

During some recent testing, we discovered that usernames in our users table are case-sensitive while usernames in LDAP appear to be case-insensitive. We are currently saving the username as it is typed by the user while logging in rather than the username that comes back from the auth service.

As a result, on a venue with LDAP authentication enabled, I can login as either delany or DELANY and either of these will work - however, this will create two different users in the Aerie database that are both associated with the same LDAP user.

Per discussion in Slack, the response from the LDAP/other auth server should contain a "canonical" version of the username, and this is the version we should store in our database, rather than the exact input provided by the user. Of course in environments with no authentication enabled, this is not possible and we should fallback to saving the user's input.

Reproduction

1. Open an Aerie environment that is configured to work with LDAP auth, or configure your local environment to use it - see https://github.com/NASA-AMMOS/aerie-gateway/pull/64 and https://github.com/NASA-AMMOS/aerie/issues/1279 for setup instructions.
2. Login to Aerie with a lowercase version of your username
3. Logout
4. Login to Aerie again with an uppercase version of your username
5. Check the Aerie database and see that two users with your username exist

Severity

Minor