get https://api.quickblox.com/users/external/.json
Retrieve a user by External User IDExternal User ID - a unique identifier of the user in the integrated external system; used for cross-referencing. For example, a user has an internal user ID within the QuickBlox system and external ID, provided by the integrated external (client) system. When an API call with reference to the user has to be submitted, the user can be referenced by either internal or external identifiers..