https://www.centos.org/docs/5/html/Deployment_Guide-en-US/s1-httpd-secure-server.html#private-signed-cert

https://www.linode.com/docs/security/ssl/ssl-certificates-with-apache-2-on-centos

Converter chaves:
http://stackoverflow.com/questions/8774574/how-can-i-convert-a-pfx-certificate-file-for-use-with-apache-on-a-linux-server

Mais do que um certificado por domínio:
http://serverfault.com/questions/392149/domains-and-subdomains-virtualhosts-with-different-ssl-certificates

https://www.digicert.com/ssl-support/apache-multiple-ssl-certificates-using-sni.htm

https://www.digicert.com/ssl-certificate-installation-apache.htm