title: Confused with OAuth 2.0 in flutter
body: <p>I am trying to develop a Flutter app, with which users can login with their Square account credentials, and I can use OAuth2.0 to get their access token, and use it to make calls to the Square API.</p>
  <p>I am confused with the whole flow: after the users sign in with their Square credentials, how do I get their client secret/ app id (which are required for the obtaintoken API call). To get the access token I need those, but there doesn't seem to be any functionality for that. Right now I am testing by hardcoding both in a .env file, but how to do it for an end user? I'm currently using FlutterAppAuth.</p>