MongoDB’s handshake protocol was designed in 2016 to allow client metadata to be recorded in a mongos or mongod log about the environment an application was connecting from. This was expanded in 2019 to support capturing additional details about libraries that wrap MongoDB’s drivers - such as ODMs or framework integrations.

This expansion was sufficient for scenarios where a MongoClient was being instantiated directly within the wrapping library or integration, however when those environments instead take an instance of a MongoClient as a parameter, there is no way to record further metadata by (re)sending the initial handshake.