Support cert/key export formats

[zeroXten]

E.g. PKCS8, combined etc.

[zeroXten]

Example of requiring PKCS8:
http://basildoncoder.com/blog/postgresql-jdbc-client-certificates.html

[zeroXten]

Chained certs for nginx:

http://nginx.org/en/docs/http/configuring_https_servers.html#chains

"The server certificate must appear before the chained certificates in the combined file"