User Configuration > Administrative Templates > Skype for Business 2016 > Microsoft Lync Feature Policies
User
HKCU\software\policies\microsoft\office\16.0\lync
When Lync connects to the server, it supports various authentication mechanisms. This policy allows the user to specify whether Digest and Basic authentication are supported. Disabled (default): NTLM/Kerberos/TLS-DSK/Digest/Basic Enabled: Authentication mechanisms: NTLM/Kerberos/TLS-DSK Gal Download: Requires HTTPS if user is not logged in as an internal user.