Auth0's rule to create an user credential for users who logged in with social accounts

rule.js

function(user, context, callback) {
  var request = require("request");

  function mergeProcess({ primaryUser, toMergeUser }) {
    var provider = toMergeUser.identities[0].provider;
    var providerUserId = toMergeUser.identities[0].user_id;

    var userIdentitiesEndpoint =
      auth0.baseUrl + "/users/" + primaryUser.user_id + "/identities";

    return new Promise(function(resolve, reject) {
      request.post(
        {
          url: userIdentitiesEndpoint,
          headers: {
            Authorization: "Bearer " + auth0.accessToken
          },
          json: { provider: provider, user_id: String(providerUserId) }
        },
        function(err, response, body) {
          if (err) reject(err);
          if (response && response.statusCode >= 400) {
            reject(
              new Error("Error linking account: " + response.statusMessage)
            );
          } else {
            resolve();
          }
        }
      );
    });
  }

  function createUserPasswordConnection({ email }) {
    return new Promise(function(resolve, reject) {
      var ManagementClient = require("auth0@2.9.1").ManagementClient;
      var managementClient = new ManagementClient({
        domain: auth0.domain,
        clientId: configuration.CREATE_USER_PASSWORD_MANAGEMENT_CLIENT_ID,
        clientSecret: configuration.CREATE_USER_PASSWORD_MANAGEMENT_CLIENT_SECRET,
        scope: "create:users"
      });

      managementClient
        .createUser({
          email,
          verify_email: false,
          email_verified: false,
          password: require("crypto")
            .randomBytes(32)
            .toString("hex")
            .slice(0, 32),
          connection: configuration.CREATE_USER_PASSWORD_MANAGEMENT_DATABASE_CONNECTION_NAME
        })
        .then(resolve)
        .catch(reject);
    });
  }

  var hasPasswordConnection = user.identities.find(function(identity) {
    return (
      identity.provider === "auth0" &&
      identity.connection === configuration.CREATE_USER_PASSWORD_MANAGEMENT_DATABASE_CONNECTION_NAME
    );
  });

  if (hasPasswordConnection) callback(null, user, context);
  else {
    createUserPasswordConnection({ email: user.email })
      .then(function(createdUser) {
        mergeProcess({
          primaryUser: user,
          toMergeUser: createdUser
        })
          .then(function() {
            console.log("succeeded");
            context.primaryUser = user.user_id;
            callback(null, user, context);
          })
          .catch(function(e) {
            console.log("failed", e);
            callback(e);
          });
      })
      .catch(function(e) {
        console.log("failed", e);
        callback(e);
      });
  }
}