Github user IsurangaPerera commented on the issue:
https://github.com/apache/syncope/pull/70
A validation error will be raised in the worst case(As I see the thread
safe problem won't just affect the login as we discussed Saml as well. So
Unique constraint will only prevent those scenarios. the advantage is the
validation error is the worst case. It won't negatively affect the flow of the
system like in thrad safe problem(Users being blocked from login)---
