expressjs + mongoose + passportjs GithubStrategy

I'm trying to save a user that authenticated through GitHub into mongodb. I'm using mongoose. Below is what I have:

var accountSchema = new Schema({
  firstName: String,
  lastName: String,
  email: String,
  githubId: String,
  githubAccessToken: String
});

passport.use(new GitHubStrategy({
    clientID: config.GITHUB_CLIENT_ID,
    clientSecret: config.GITHUB_CLIENT_SECRET,
    callbackURL: "http://127.0.0.1/auth/github/callback",
    scope: ['user', 'public_repo', 'repo', 'gist']
  },
  function(accessToken, refreshToken, profile, done) {
     User.findOrCreate(...) // User is not defined
  });
}));

How do I save a user to mongodb so they don't have to authenticate each time they visit the site? The example on the passport-github doesn't save anything to a database, which is what I'm looking to do? Are there any tutorials regarding this?