Access Control Service, otherwise known as ACS, is officially being retired. ACS will remain available for existing customers until November 7, 2018. After this date, ACS will be shut down, causing all requests to the service to fail.
This announcement affects any customer who has created one or more ACS namespaces in their Azure subscriptions. It may also affect customers of any service that uses ACS as a means of authentication. Examples of such services include Azure Service Bus, Azure Relay, Azure Media Services, and Azure Backup. In accordance with this announcement, Azure Service Bus and Azure Relay will be officially deprecating support for ACS on November 7, 2018.
Read about it in the Azure blog.