If an existing session is active at the time of launch, that user id
appears in the user_updated log. This log should show the launching user
updating their own record, not someone else. To resolve this, auth the
user before making any record updates so that the event gets the correct
user id.
Three modes are initially introduced here, for use by dependent code:
1. Automatic - where accounts will be automatically created for users
2. Prompt new or existing - where the user can choose to use an existing
account or have a new account created for them.
3. Prompt existing only - where users must link an existing account.
This change also adds linked logins, for use with provisioning.
Jake Dallimore