get https://stagingaccount.xoxoday.com/chef/v1/oauth/token
One you've generated the access token, this article explains how you can validate the access token.
At any point, if you want to validate if the access_token is valid or not, then you can call the endpoint as outlined on this page. The client application will pass the bearer token in the header. The response to the request will be as outlined on the right-hand side panel.