Getting a Parse.User for an authenticated Facebook user.

gistfile1.js

function authenticateParseUser(authResponse) {
  Parse.FacebookUtils.logIn({
    id: authResponse.userID,
    access_token: authResponse.accessToken,
    expiration_date: moment().add('s', authResponse.expiresIn).format()
  }).then(function(user){
    /* Do useful stuff with your new Parse.User */
  }, function(error){
    /* Something went wrong with the authentication */
  });
}

Note that I'm using moment.js to convert from an expiresIn timestamp to a Parse compatible date format.