Some applications require to do correlation/merge of collected data between endpoints that belong to same user.
For example, this may be sensors in one house that belong to same user, or various fitness/health tracking apps/devices.
In order to correlate this data, user can introduce some user id into the log schema. However, this is potential security issue, due to some hacked app may log data from different user name.
In order to avoid unnecessary security risks, we need to add verified user id to the log appender API.