With 078698fdf4 the semantics of the
ListRoleAssignments Call in the settings service change. It no
no longer returns a "not found" error when there is not RoleAssignment
for a user. We'll just get an empty list as the result.
This changes the behaviour of the default role assignment to work with
the new semantics.
When using an external user management we need to allow users to self-assign
the default role. This adds an explicit check for that to the settings service.
This also means we no longer need to fiddle with the account id in the proxy
upon first login.
Fixes: #5045
