Proxy to upstream HTTPS server *with different* keys/certs in nginx

[tbamise]

> 
> Connections to upstream servers don't use any client certificates.
> 

Yes I agree. The connection to the upstream server uses the nginx server
certificates specified by $ssl_certificate(_key).
Basically I want to use:
for downstream to client - a.cert & a.cert.key for connection to clients
for upstream to upstream servers - b.cert & b.cert.key for connection to
upstream servers.

The https & server modules of Nginx only allow you to specify a single cert
pair via $ssl_certificate(_key)

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,247305,247311#msg-247311