code: def login(username, password)
        response = request_json(
          '/api/v1/login',
          method: :post,
          body: {
            username: username,
            password: password
          }
        )
        Session.new self, Token.new(response['data'])
      end
docs: Login REST API
   @param [String] username Username
   @param [String] password Password
   @return [Session] Rocket.Chat Session
   @raise [HTTPError, StatusError]