How to access to access_token in json config for app studio?

HI, I am trying to build a studio app to connect AC with a third-party app. However, this app set oauth api a little bit different. For example, it requires access token to be put in header “Access-Token” which is not “Authorization”. As a result, I will need to manually set this header with the access_token. So I am just wondering how can I get the stored access_token in json config? Is it stored in some variables after users connecting?
Thank you very much!