Refer to IBM's Digital Certificate Manager documentation for information on how to create an SSL certificate in IBM Apache at http://publib.boulder.ibm.com/infocenter/iseries/v7r1m0/topic/rzahu/rzahu.pdf.
Once the SSL certificate is created, add the following lines to the Zend Server Apache configuration file (located in '/www/zendsvr/conf/httpd/conf'):
##
SSL start
LoadModule ibm_ssl_module /QSYS.LIB/QHTTPSVR.LIB/QZSRVSSL.SRVPGM
Listen *:443
SSLEngine On
SSLAppName <SSL Application created by the SSL wizard>
SetEnv HTTPS_PORT 443
## SSL end