Support anonymous join fallback for conferences

[kvanopdorp]

I sometimes have a need to join meetings as an external participant, i.e. participating in a meeting with an organization where I don't have an account or am not federated. According to this pretty detailed document, to do this the client must support anonymous join fallback.

https://blogs.technet.microsoft.com/scottstu/2015/04/03/anonymous-join-from-skype-for-business-and-lync-clients/

I'm seeing in the debug logs the expected 504 response code that the document notes but pidgin does not respond by trying an anonymous join process. The ms-diagnostics in my case does not come back with the noted 1017 code but rather 1034

ms-diagnostics: 1034;reason="Previous hop federated peer did not report diagnostic information"

If fallback is not simple, maybe a checkbox when joining a meeting to do so anonymously would be another option though a fallback mechanism would be cleaner.

I've started looking at the source code but it could take me a while to figure out any kind of patch. If anyone has any ideas before I do, I am happy to test.

[msbentley]

This would be great! My organisation has just moved to SfB and pidgin+SIPE works fine for me, but some of the external teams we work with have linux users, and they are currently out of luck...

[edbennett]

I'm also hitting this; if anonymous join can't be implemented, it would be an improvement if the error message generated indicated what the problem was, since the current message is not helpful.