What is the Access Control Service?
The Microsoft Azure Access Control Service (or ACS) is a cloud-based service that provides a way of authenticating and authorizing users to gain access to web applications and services.
Changes to How Access Control Service Namespaces are Created
New ACS namespace creation will be restricted starting June 30th, 2017. If you need to create an ACS namespace beyond this date, you will need to call Azure customer support.
Read more about it on the Azure blog.