Facebook Reconcile Lambda

When a Facebook identity provider is used to complete a federated login request, FusionAuth will use the configured linking strategy to reconcile the user. FusionAuth will attempt to match the user information returned from the Facebook identity provider to an existing user account or create a new one.

You may optionally utilize a lambda to customize the user and user registration during the authentication event.

When you create a new lambda using the FusionAuth administrative user interface, you will be provided an empty function to implement.

Lambda Structure

If you are using the API to create the lambda you will need to ensure your function has the following signature:

function reconcile(user, registration, facebookUser) {
  // Lambda code goes here

This lambda must contain a function named reconcile that takes three parameters. The parameters that the lambda is passed are:

  • user - the FusionAuth User object. You can modify this, except the email or username attribute may not be modified after the user has been linked.
  • registration - the FusionAuth UserRegistration object. You can modify this.
  • facebookUser - the User returned from the Facebook Me API. This is read-only.

The two FusionAuth objects are well documented here in the User API and Registration API documentation. The facebookUser may contain various user claims depending upon the user’s Facebook configuration.

Assigning The Lambda

Once a lambda is created, you may assign it to the Facebook identity provider in the IdP configuration.

Navigate to Settings -> Identity Providers and select your existing Facebook configuration or click Add provider and select Facebook if it has not yet been configured.

Default Lambda

A default Facebook reconcile lambda is available in FusionAuth that may be used or modified. The default Facebook lambda function is documented below.

// This is the default Facebook reconcile, modify this to your liking.
function reconcile(user, registration, facebookUser) {
  // Un-comment this line to see the facebookUser object printed to the event log
  // console.info(JSON.stringify(facebookUser, null, 2));

  user.firstName = facebookUser.first_name;
  user.middleName = facebookUser.middle_name;
  user.lastName = facebookUser.last_name;
  user.fullName = facebookUser.name;

  if (facebookUser.picture && !facebookUser.picture.data.is_silhouette) {
    user.imageUrl = facebookUser.picture.data.url;

  if (facebookUser.birthday) {
    // Convert MM/dd/yyyy -> YYYY-MM-DD
    var parts = facebookUser.birthday.split('/');
    user.birthDate = parts[2] + '-' +  parts[0] + '-' +  parts[1];