How to add custom fields in OAuth2 access token from a target endpoint

[#1]

I am trying to reuse the OAuth2 token generation from the edge, but add custom fields into the generated token. I see plenty of example of using an external token generator, but I don't want to generate the whole token, just my custom fields from a target endpoint. I looked at using SetOAuthV2Info, but still not clear how to receive the generated token in my nodeJS target and then add my custom fields before returning the results. (I'll be using some request headers in the target endpoint to generate the custom fields). Appreciate the help.