How to gain access to an ArcGIS-Server WMS-Mapservice when the service directory folder is password protected?

[RobertBuckley1]

In ArcGIS Server 10.9 server managerI have a password protected folder containing a map-service with wms capabilities. How can I now gain access to the WMS Service und the GetCapabilities document? I tried using the "&user=xxx&password=XXX" arguments in the url,but the response has a status 499 - not authorized.

ArcGIS Server is using ADAP for it's user management.