instead of looking linked user by email because :
- follows FC recommendation to fetch ds account by openid
- the email is not a valid key as many user can share the same FCI email.
The following scenario is now working
A user A (email: 1@mail.com) uses FC to connect to DS
=> It is connected as 1@mail.com
Another user B (email: generic@mail.com) uses FC to connect
=> It is connected as generic@mail.com
The first user A change its FC email to generic@mail.com and connect to DS
=> It is still connected as 1@mail.com
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