3rd party integration best practices/problems

Hey Chris!

I was wondering about the differences of the implementations of complex 3rd party integrations. For instance on the one hand there is segment.io or intercom.io. For these to work you need to track either with js or ruby the user actions. On the other hand there is for instance trello or slack integration where you send over data when user triggers a post/patch request like commenting on something or joining as team member. (Stripe or Braintree could be a 3rd example, where authentication/authorization is super crucial but those are documented well everywhere and you also made great screencasts on those)

Could you write a high level explanation what the main similarities and differences are? (design considerations (db tables/ models / controllers/ user flow), implementation problems, etc.) It would be also great to see some screencasts on these topics. I know this question is a bit broad, but I couldn't find good resources on this topic and having hard time figuring out how to integrate these.