Lync 2013 client popup credentials are required for Outlook

When we started migrating users to Exchange 2013 and Lync 2013, users began complaining of being prompted to enter their credentials for Outlook when starting Lync.

The exact error message is:
Credentials are required
Lync needs your username and password to connect for retrieving calendar data from Outlook

We did some Wiresharking and found this to occur when Lync was connecting to the EWS and Autodiscover Exchange URLs.



The Solution

1. Ensure your internal and external EWS/Autodiscover URLs are in the Internet Explorer local intranet zone. This will be extremely helpful in assisting you to troubleshoot the problem.

2. Logon to your Exchange server and open IIS.

3. Click the EWS directory under "Default Web Site".

4. Open Authentication, click Windows Authentication and then Providers.

5. Remove all entries except for NTLM.

6. Repeat the same for the Autodiscover directory.

7. Restart IIS.

Now restart your client and you should no longer be prompted for Outlook credentials.



Additional troubleshooting tips

Internet Explorer debug tools are great for troubleshooting authentication issues, but first ensure your EWS/Autodiscover URLs are in the Internet Explorer local intranet zone.

A simple test is to go to the EWS URL (http://yourdomain/EWS/exchange.asmx) in Internet Explorer, it should automatically negotiate authentication and show you the service page. If you don't receive the "You have created a service" page then your single sign on is not correctly configured.

1. Open Internet Explorer and press F12 to launch the debug tools.

2. Click Network and "Start Capturing".

3. Now open your EWS URL: http://yourdomain/EWS/exchange.asmx

4. Click "Stop Capturing" and click "Go to detailed view"

You can see the order of the authentication providers and any issues that might have occured during authentication. You can then repeat the same for Autodiscover, remember if Autodiscover can't negotiate pass through authentication then it will prompt the Lync user for credentials.