I am creating the application based on Telsla, I am wondering how to make authentication of a user, how to check if access token valid and not expired. I know how to create a new token from client secret and client id, but how to check if a token is correct, what URL to use, and what should be in the body of the request. Thanks
You can call Get Token request each time and it will give you the latest active token or generate a new one should it be needed.
Have you checked out our SDKs and sample code on github.com/telstra also the getting docs and the started section for the API you are using?