This is about using Magento 2 internal classes useful for building restapi client in your magento extension.
\Magento\Framework\Oauth\Oauth
Oauth class will help you deal with REST authorization. Interesting function is `buildAuthorizationHeader` . Of course you should inject \Magento\Framework\Oauth\OauthInterface in your code instead of the class.
\Magento\Framework\Serialize\Serializer\Json
For building valid json…