As admin, go to Site administration ►Users ►Accounts ►User profile fields. Create a new profile field of any type. Make sure to add an underscore (_) in the short name and enable "Display on signup page?". E.g. the short name can be "my_new_field". Go to Site administration ►Plugins ►Authentication. Enable "Email-based self-registration". Now, open a Terminal/Console and execute the following curl command (replacing the site URL with yours) curl 'http://localhost/stable_master/lib/ajax/service.php' --data-binary ' [{"index":0,"methodname":"auth_email_get_signup_settings","args":{}}] ' | python -m "json.tool" Check that no error is returned and the field you created is included in the "profilefields" field of the response.