There are two issues regarding login by email:

• email may not be unique,
• you can register user with a login that resembles email and prevent login for different user.

We need to:

• provide Command to do the audit of User database and identify possible issues (non-unique emails already in database, or logins that resembles email if login by email is enabled),
• provide an option to enable/disable email uniqueness during registration,
• provide a configurable pattern option to prevent some login types during registration (like ie. ones that can be valid email).