def update_access_token(response)
      h = JSON.load(response)
      @access_token = String(h['access_token'])
      @access_token_expires_at = Time.at(Time.now.to_i + Integer(h['expires_in']))
    end
def update_access_token(response)
      h = JSON.load(response)
      @access_token = String(h['access_token'])
      @access_token_expires_at = Time.at(Time.now.to_i + Integer(h['expires_in']))
    end
Sets the @access_token and @access_token_expires_at