MISP AuthKey edit endpoint allows authenticated user email enumeration

An information disclosure vulnerability exists in the MISP AuthKey edit functionality. When a validation error occurs during an AuthKey edit request, the user dropdown was populated using the attacker-controlled AuthKey.user_id value from the submitted request data. An authenticated user with permission to edit an AuthKey could submit arbitrary user IDs and observe the returned dropdown data, allowing enumeration of user email addresses. The issue is fixed by deriving the dropdown user from the persisted AuthKey owner instead of the request body.