Ability to customize the logger

Sixt has thousands of users and optimizely currently logs in unstructured manner. We would like to include some custom fields for each request that comes into our servers in order to facilitate easier logging, review and optimizely logs search. As currently, we have no way to see all the logs for each of our users as Optimizely logging is not concurrency safe. Currently, if we wish to add internal data to optimizely logging, this does not work and presents quite a big issue for us in terms of debugging and testing as we cannot search for a request and see optimizely logs but have to do a separate search, based on user id which makes it difficult.