Migration to LDAP Authentication

Hello,
We've been using projeqtor for a while, in our PMO department and we've created some users directly into projeqtor (while creating resources or contacts, some were also checked as users, and of course the users in the PMO). The good part of it is that we've created those users with their domain username (LDAP username).
Now, we'd like to rollout projeqtor to all project members and decided to activate the LDAP integration and we would like to allow the users already created (via projeqtor) to authenticate through LDAP, nor duplicating the user list neither deleting those records (which would request to remove/change all records already associated with that user).
Is there any way (database update, or something like that) to make projeqtor understand that the user (previously inserted via projeqtor) is now using LDAP authentication?

Thank you very much.