Allow using the user created by the Apps Engine to perform Rest request

[Cuong Huu Nguyen]

As we allow create bot user with the Apps Engine, we might need to use that user to call some API requests. That will allow the Apps to perform more tasks like querying the rooms / users with pagination.

There are 2 ways that we could support it:

• Allow passing password along with the user data
• Allow getting the BOT user access token