When using an Identity Provider (GitHub, GitLab, Azure DevOps, etc.), the login generated by SonarQube has no interest for the user, and it should not be the responsibility of the plugin to specify the format of this login.
In settings of identity providers (Administration -> Security), all settings Login generation strategy should be removed.
In the Java Authentication API used by community plugins, UserIdentity#setLogin should be deprecated as it won't have any effect anymore.
This web service is used to update the login used by SonarQube. When the user is a local one or a user created by a Realm (eg LDAP), the provider login should now also be updated