A description of the new HttpProxyControlFlags GPO settings in the registry

After you apply one of the following security updates, a new HttpProxyControlFlags Group Policy Object (GPO) is added to resolve Microsoft Office O365 authentication issues:

• December 8, 2015 security update (KB3114351) for Microsoft Lync 2013 (Skype for Business)
• December 8, 2015 security update (KB3114372) for Skype for Business 2016

These issues occur in Microsoft Lync 2013 or Microsoft Skype for Business 2015 or 2016 organizational environments that use HTTP proxy service, enable automatic detection feature by setting proxy auto-configuration (PAC) files or equivalent mechanism), or use a proxy service that requires authentication.

In these environments, a Lync 2013 or Skype for Business client uses the correct proxy settings to sign in to Office 365 by using Microsoft Online Services Sign-In Assistant (MOS SIA) Identity Client Runtime Library (IDCRL). However, in some environments in which Lync 2013 or Skype for Business client is running behind two or more proxies, Skype for Business can choose the wrong proxy settings for IDCRL to use. This may block the authentication or otherwise require additional proxy authentication. To resolve this situation, you can use this GPO setting to resolve the authentication issues.