WebapiSecurity enables access management of some Web API resources. If checkbox is enabled in backend through: Stores -> Configuration -> Services -> Magento Web API -> Web Api Security then the security of all of the services outlined in app/code/Magento/WebapiSecurity/etc/di.xml would be loosened. You may modify this list to customize which services should follow this behavior. By loosening the security, these services would allow access anonymously (by anyone).