Passport Callback Function

Passport Callback Function

After Google authenticates the user, Passport calls your callback function with the user's profile data. This is where you decide what to do — check if the user exists, save them to a database, or create a session.

The Callback Function

passport.use(
    new GoogleStrategy({
        clientID: keys.google.clientID,
        clientSecret: keys.google.clientSecret,
        callbackURL: '/auth/google/redirect'
    }, function(accessToken, refreshToken, profile, done) {
        // This fires after Google sends back the user profile
        console.log('Access Token:', accessToken);
        console.log('Profile:', profile);
        console.log('ID:', profile.id);
        console.log('Name:', profile.displayName);
        console.log('Photo:', profile.photos[0].value);
    })
);

Callback Arguments

Argument	Contains
accessToken	Token to access Google APIs on behalf of the user
refreshToken	Token to get a new access token when it expires
profile	The user's Google profile data (name, email, photo)
done	A function you MUST call to continue the auth flow

The Profile Object

{
    id: '123456789',
    displayName: 'Shaun Pelling',
    name: { familyName: 'Pelling', givenName: 'Shaun' },
    emails: [{ value: 'shaun@gmail.com', verified: true }],
    photos: [{ value: 'https://lh3.googleusercontent.com/photo.jpg' }],
    provider: 'google'
}

Calling done()

function(accessToken, refreshToken, profile, done) {
    // Check if user exists in database
    // If not, create the user
    // Then call done:
    done(null, user);  // null = no error, user = the user object
}

done(null, user) tells Passport the authentication succeeded and passes the user object forward. Passport then serializes the user for the session.

Key Takeaways

• The callback fires after Google authenticates the user and Passport gets the profile
• profile contains the user's Google ID, name, email, and photo
• You must call done(null, user) to complete the authentication process
• This is where you save or retrieve the user from your database