If your users are in AD, but you can’t use windows authentication, consider using username authentication
Jason Taylor, Prashant Bansode, Carlos Farre, Madhu Sundararajan, Steve Gregersen
Using Username client authentication option, the username/password combination will be automatically mapped to Windows account. By using username authentication with Windows, you benefit from a unified identity store, centralized account administration, enforceable
account and password policies; additionally it will work in an Internet configuration where the client and server do not have access to an AD server.
You have to ensure that the user credentials passed over the network are secured using the message security.