Oauth2 flow without redirect_uri

Question

I am creating an Android/iOS app which communicates with a Node.js server and would like to identify them securely on my server using Google (and/or Facebook) and OAuth2. I\

Answer 1

TL;DR How do you use OAuth2 to authenticate users between my client and my server without redirection?

You can't. OAuth requires that the user is directed to an authorization (and possibly login) screen, and then redirected back to your app.