Can’t join online meeting that is created in a non-federated organization by using Lync 2013

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Microsoft Lync 2013 More...Less

Symptoms

Consider the following scenario:

You deploy a proxy server that only support basic authentication in an organization. There is no DNS resolvers for Internet server in the organization.
A Microsoft Lync 2013 user (user A) in the organization receives a meeting invitation from another user (user B). User B is in an organization that is not federated with user A’s organization.
User A tries to join the meeting.

Note To do this, user A must access Internet through the proxy server.

In this scenario, Lync 2013 keeps trying to connect to the meeting instead of prompting user A for credentials.