Symptoms
When a Mac user tries to log on to the Conferencing Dial-In Page in Microsoft Skype for Business Server 2015 from the internal network, the user receives the following error message:
Note
Cannot sign in because your Web Browser does not support the authentication method used by the server. Contact your system administrator for assistance" on Mac computers
Resolution
To fix this issue, install June 2016 cumulative update 6.0.9319.259 for Skype for Business Server 2015, Web Components Server.