Uploading a file over SSL with Client Side Certificate and Android's HttpsURLConnection
Not an answer, more a work-around, for your reference.
After bashing our heads around this issue, and doing a lot of research, we gave up. We've opened this issue with Google, and implemented the following work around:
In order to upload a file, the app first gets an Upload Token via an endpoint that requires the client-certificate, and afterwards uses this token to upload to an endpoint that doesn't require the client certificate (but still over SSL (Https)).
Yes, it's a minor breach of security, but we had to do it. We've protected it as much as we could.
I promise to update when the Google's ticket will be updated (and hopefully resolved).
It's a bit late (as you already implemented a workaround) but this should solve the problem: https://stackoverflow.com/a/9224892/1619545
We're experiencing the same issue, setting the client cert negotiate flag to enabled seems to be the only thing hat helps. Have a look here for a way how to change the flag at the cert binding:
http://help.sap.com/saphelp_smp305svr/helpdata/en/6f/f0a9b6e1c743d48d1e57235d297c1c/content.htm