From a user account that is a member of the RTCUniversalServerAdmins group (or has equivalent user rights), or assigned to the CsServerAdministrator or CsAdministrator role, log on to any computer that is in the network in which you deployed Lync Server 2010.

Open a browser window, and then enter the Admin URL to open the Lync Server Control Panel. For details about the different methods you can use to start Lync Server Control Panel, see Open Lync Server Administrative Tools.

In the left navigation bar, click Security and then click Web Service.

On the Web Service page, click a configuration, click Edit, and then click Show details.

In Edit Web Service Setting, in Windows authentication, select Negotiate, NTLM, or None.

Select one or more of the following depending on the capabilities of the clients and support in your environment:

• Enable PIN Authentication to enable clients to be authenticated using PIN numbers.
  
  
• Enable certificate authentication to have the servers in the pool issue certificates to clients.
  
  
• Enable certificate chain download to have servers presented with an authentication certificate download the certificate chain for that certificate.
  
  
• Show Lync Attendee download link to give the users the option to download Lync 2010 Attendee.
  
  
• Show the link for user to join meeting using legacy client to give users the option to join meetings using a previous version of Communicator.
  
  

Click Commit.