How to implement Steam Auth with Firebase?

Question

How to implement Steam Auth with Firebase?

All I found is the old answer:

https://groups.google.com/forum/#!topic/firebase-talk/rApG8QQd6t4

Does SOER know any information or can a Firebase engineer give a more detailed answer?

I am currently trying to authenticate a user on Steam using this library:

https://github.com/liamcurry/passport-steam

and then use custom Firebase tokens to get the user on my Firebase authentication system.

I do not know if this is the right approach. Despite this, I am stuck.

EDIT:

Here is my current code:

app.js

var passport = require('passport');
var SteamStrategy = require('passport-steam').Strategy;

app.use(passport.initialize());

passport.serializeUser(function(user, done) {
  done(null, user);
});

passport.deserializeUser(function(obj, done) {
  done(null, obj);
});

passport.use(new SteamStrategy({
    returnURL: 'http://localhost:8080/users/steam/return',
    realm: 'http://localhost:8080/',
    apiKey: steamKey.steam,
    stateless:true
  },
  function(identifier, profile, done) {

    profile.identifier = identifier;
    return done(null, profile);
  }
));

users.js

    router.get('/steam', passport.authenticate('steam', { failureRedirect: 'login' }), function(req, res, next) {

});

router.get('/steam/return', 
  function(req, res, next) {
      req.url = req.originalUrl;
      next();
  }, 
  passport.authenticate('steam', { failureRedirect: 'users/login' }),
  function(req, res) {
    console.log(JSON.stringify(req.query));
    var oid = req.query["openid.claimed_id"];
    var array = oid.split("/id/");
    console.log("Array: "+array);
    var result = array[1];
    console.log(result);
    admin.auth().createCustomToken(result)
      .then(function(customToken) {
         res.render("users/login",{token: customToken, passed: true});
      })
      .catch(function(error) {
        console.log("Error creating custom token:", error);
      });
});

users /login.ejs:

<a href="steam"><img id="steamLogin" src="../../public/assets/steamLogin.png"/></a>
    <script>

        if ("<%=passed%>" == "true") {
            firebase.auth().signInWithCustomToken("<%=token%>").catch(function(error) {
                if (error) {
                    alert(error);
                }
                else {
                    res.redirect("screenshots/index");
                }

            });   
        }  

    </script>