If you are simply wanting to post form data via HTTPS, Apache should be able to handle that for you. However, if you are wanting to use OpenSSL and PHP to generate key pairs and encrypt data, this two-part article that I wrote might be of use to you:
http://3stepsbeyond.co.uk/company-blog/coding/openssl-and-php-part-one
http://3stepsbeyond.co.uk/company-blog/coding/openssl-and-php-part-two
