It seems that the current implentations for SSL request do not support Mutual SSL authentication. Current outgoing requests do not use the javax.net.ssl.keyStore when making requests, which prevents the 2-way ssl handshake from going through.

The Apache ApacheHttpTransport (UPDATE: this should really have been referred to v2 ApacheHttpTransport, although the same question applies to v1. see #904 (comment)) not using getSystemSocketFactory. That version takes into account the javax.net.ssl properties, and would most likely allow for the 2way ssl connection to complete. Is there a reason this is not being used?