The client's version, packed like QueryVersionResponse.server_version (major << 48 | minor << 32 | build << 16 | patch). May be 0. If the server administrator has set a minimum client version, older clients are refused with E_MFILES_INCOMPATIBLE_SERVER_VERSION.
LogInRequest.client_data -- Describes the client software. Set type (for example CLIENT_TYPE_SERVER_API) and language; set capabilities only for features your code handles.