Every dial in user has its RegistedUser authToken set to an empty string,
Since authToken is the RegUser's HashMap indexing key, this causes a
bunch of inconsistencies; eg.: endpoint ejection will stop working if
more than one dial-in user joined a meeting concurrently because the
later dial-in devices overwrite the earlier ones in the RegUsers map.
The authToken is now mocked as the user's intId (which, for dial-in, is
the voice user ID) so that some sort of uniqueness is guaranteed within
the voice conf scope.
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