Although the EWS service advertises OAuth settings (the authorization URI), the client ignores this and falls back to a non-MFA sign-in by using an OrgID channel.

After you sign in, Skype for Business or Lync 2013 connects to the user's mailbox in Exchange Online by using Exchange Web Services (EWS).

The Skype for Business Desktop and Lync 2013 clients connect to Skype for Business Server by using NTLM or the Kerberos authentication protocol, a user name and password, or Windows Integrated Authentication.In these scenarios, the available functionality in the previous environment is as follows:

Setting up mailboxes in Exchange Online in Microsoft 365 by using Modern Authentication and Multi-factor Authentication (MFA) with OAuth.

Setting up Lync 2013 and Skype for Business users to be homed on Skype for Business Server 2015 or Lync Server 2013 on-premises.

The information in this article helps IT and Microsoft 365 administrators in the following scenarios: This article also describes which Exchange Online and Skype for Business deployments require this setting. This article contains information about the AllowAdalForNonLyncIndependentOfLync setting in Skype for Business 2016, Skype for Business 2015, Lync 2013, and Exchange Online.

How to disable skype for business sccm