title: Firebase Authentication via OpenID Connect
body: <p>I would like to authenticate users against Firebase Authentication via OpenID Connect. In other words:</p>
  
  <ul>
  <li>create a Firebase project</li>
  <li>add users under authentication</li>
  <li>get an issuer URL for my project that implements OIDC Discovery</li>
  <li>get a clientID</li>
  <li>use the issuer URL and the clientID in my app that acts as an OIDC client to retrieve information / id_token for users in the Firebase Project</li>
  </ul>
  
  <p>The documentation does not mention this possibility, so I'd understand if this was not possible.</p>
  
  <p>However:</p>
  
  <ul>
  <li>using OIDC is quite the standard way to do these things</li>
  <li>there is <a href="https://stackoverflow.com/questions/43989039/using-firebase-openid-connect-provider-as-aws-iam-identity-provider">this</a> and <a href="https://stackoverflow.com/questions/45143700/unable-to-authenticate-using-firebase-open-id-connect-as-amazon-cognito-authenti">this</a> post that actually tell me this is/was possible</li>
  <li>the OIDC discovery document they mention is actually available my project too, although it is incomplete (missing the endpoint URLs)</li>
  <li>digging in the GC dev console it seems like OAuth2 is used internally in the Firebase SDK - newly created service accounts inherit some callback URLs that belong to my Firebase project</li>
  </ul>
  
  <p>Implementing my own IDP using Firebase Auth seems to be an overkill, especially that it might already be available.</p>
  
  <p>Any hints anyone? </p>