Explanation
The Delivery Controller runs the Secure Ticket Authority (STA) and the Citrix XML Service, which are responsible for issuing session tickets in response to connection requests for published applications and desktops on Citrix Virtual Apps and Desktops12. The Citrix Gateway can be configured to use the STA to validate the tickets and allow secure access to the resources3.
1: Access Citrix Virtual Apps and Desktops resources with the ... - NetScaler 2: FAQ: Citrix Secure Gateway/ NetScaler Gateway Secure Ticket Authority 3: Configuring the Secure Ticket Authority on NetScaler Gateway