Symptoms
After you run the Set-CsAuthConfig -Scenario BlockWindowsAuthExternally cmdlet in Microsoft Skype for Business Server 2015, the form-based authentication still works.
Resolution
To fix this issue, install the July 2019 cumulative update 6.0.9319.559 for Skype for Business Server 2015, Core Components.
More information
After you apply the July 2018 cumulative update 6.0.9319.534 for Microsoft Skype for Business Server 2015, you can use the Get/Set-CsAuthConfig cmdlets to manage the authentication configuration for your Skype for Business Server. For more information, see:
