passport-auth0: user_id is missing in profile

Hi,

i just did the nodejs/express quickstart for auth0. It seems like the user_id property is missing in req.user after a use authenticated.

const strategy = new Auth0Strategy(
  {
    domain: '',
    clientID: '',
    clientSecret: '',
    callbackURL: process.env.AUTH0_CALLBACK_URL || 'http://localhost:3000/callback',
    scope: 'openid profile email'
  },
  function(accessToken, refreshToken, extraParams, profile, done) {
    console.log(profile.user_id);   // This is undefined
    return done(null, profile);
  }
);

The docs about the profile clearly states that user_id is always available in the normalize profile: https://auth0.com/docs/user-profile/user-profile-details#normalized-user-profile

This is what i get when i print out the profile object:

{
  "displayName": "Andre Uschmann",
  "name": {
    "familyName": "Uschmann",
    "givenName": "Andre"
  },
  "picture": "https://lh5.googleusercontent.com/-KymPmQzSHZA/AAAAAAAAAAI/AAAAAAAAAAA/CSvKv_F1Xy8/photo.jpg",
  "locale": "de",
  "nickname": "andre.uschmann",
  "gender": "male",
  "_json": {
    "sub": "google-oauth2|116203000818893399355",
    "name": "Andre Uschmann",
    "given_name": "Andre",
    "family_name": "Uschmann",
    "nickname": "andre.uschmann",
    "picture": "https://lh5.googleusercontent.com/-KymPmQzSHZA/AAAAAAAAAAI/AAAAAAAAAAA/CSvKv_F1Xy8/photo.jpg",
    "gender": "male",
    "locale": "de",
    "updated_at": "2017-08-02T06:45:28.070Z"
  },
  "_raw": "{\"sub\":\"google-oauth2|116203000818893399355\",\"name\":\"Andre Uschmann\",\"given_name\":\"Andre\",\"family_name\":\"Uschmann\",\"nickname\":\"andre.uschmann\",\"picture\":\"https://lh5.googleusercontent.com/-KymPmQzSHZA/AAAAAAAAAAI/AAAAAAAAAAA/CSvKv_F1Xy8/photo.jpg\",\"gender\":\"male\",\"locale\":\"de\",\"updated_at\":\"2017-08-02T06:45:28.070Z\"}"
}

It seems like the user_id is stored in profile._json.sub? But this is nowhere mentioned in the docs.

Am i missing something?