Assume that you sign in to the Skype for Business client by using an external network. When you switch from the external network to an internal network, you may be repeatedly prompted to provide a user name and a password to connect to Exchange.
This issue may occur in Microsoft Skype for Business 2016 and Skype for Business 2015 (Lync 2013).
The OAuthUsed registry key can't reset if a cached web ticket is used for authentication.
To fix this issue, you first have to create a GPO to add a new DWORD registry key EnableRestoreOAuthUsedKeyWhenUsingCachedWebTicket and set the value of the key to 1 under one of the following paths:
Then, install one of the following updates:
- For Skype for Business 2016, install the February 6, 2018, update (KB4011662).
- For Skype for Business 2015 (Lync 2013), install the February 6, 2018, update (KB4011678).
Note Lync 2013 was upgraded to Skype for Business in April 2015.