code: private function createBearerCredentials()
      {
          //URL encode the consumer key and consumer secret
          $consumerKey = rawurlencode($this->credentials->getConsumerKey());
          $consumerSecret = rawurlencode($this->credentials->getConsumerSecret());
  
          //create bearer token credentials by concatenating the consumer key and consumer secret, seperated by a colon.
          $bearerTokenCredentials = $consumerKey . ':' . $consumerSecret;
  
          //base64 encode the bearer token credentials
          return base64_encode($bearerTokenCredentials);
      }
docs: Creates and returns an encoded bearer token credentials to be used for making calls to Twitter.
  
  Currently:
  - URL encode consumer key and consumer secret
  - Create bearer token credentials
  - Base64 encode the resulting value and return.
  
  @link https://dev.twitter.com/docs/auth/application-only-auth Bearer Token Description
  
  @return string base64 encoded bearer token.