Custom Claims For 3rd Party Okta Integration

Im currently working on injecting custom claims into the jwt token after login with okta. Basically, in the golang example, when coming to AuthCodeCallbackHandler via /authorization-code/callback im looking to add things like role, email, company id, etc. I wasnt able to find an example that didn’t require access to the okta account to provide those custom claims. So im just looking for direction.

Is it possible to add these claims dynamically even though I don’t own the okta application that folks are authentication against? If so, any examples floating around?