code: public function createBearerToken()
      {
          //get bearer token credentials - to be used for getting the bearer token from Twitter.
          $bearerCredentials = $this->createBearerCredentials();
  
          //Required Headers
          $headers = array(
              'Authorization' => 'Basic ' . $bearerCredentials,
              'Content-Type' => 'application/x-www-form-urlencoded;charset=UTF-8'
          );
  
          //Required Body
          $body = 'grant_type=client_credentials';
  
          //Send a Post request to `oauth2/token` and convert the resulting JSON to assoc-array.
          $data = $this->guzzleClient->post(
                  Config::get('oauth2_token'),
                  array(
                      'headers' => $headers,
                      'body' => $body
                  )
              )->json();
  
          //Set the bearer token in the AppCredentials object
          $this->credentials->setBearerToken($data['access_token']);
  
          //Return the current object
          return $this;
      }
docs: Calls Twitter and gets a bearer token. This bearer token is valid until it gets invalidated.
  
  @link https://dev.twitter.com/docs/auth/application-only-auth Bearer Token Description
  
  @return $this AppConnection