We won't implement user management functionality in lcb. This is simple enough to do with the REST API directly, and other SDKs don't need to wrap lcb for this.
LCB does implement some management functionality, however it only does so when it saves time/effort for wrappers (e.g. where internal retries and such are needed). In such situations we implement it in LCB not for end-user consumption but to eliminate the need for multiple SDKs to implement the same logic multiple times. So for example, lcb implements index management functionality.
Even when lcb does implement management functions, it is only done partially, as a JSON-encoded object is required upon input.