This is the best way I know of.
You will use a text editor (or nano if you enjoy the command line) to modify the conf file generated by the Server.app. I like using the free Text Wrangler from BareBones. BBedit is awesome if you want to pay for it.
1) First create your domain in the Server.app for use with your cert on port 443. Locate the config file. Mine is stored in /private/etc/apache2/sites/0000_any_443_yourdomainname.conf. If you specify a speficic IP address, the IP address will be there instead of the word "any" (0000_xxx.xxx.xxx.xxx_443_yourdomainname.conf).
2) Once you have the file open, add another VirtualHost wrapper which specifies port 80. Save the file and you're good to go. See example below.
TIP: You may want to copy the default port 80 confing file found in that same folder in order to easily create the port 80 VirtualHost for the 2nd step
TIP: MAKE A COPY OF THE FINAL FILE SOMEWHERE! The Server.app will sometimes overwrite it when new domains are added or other changes are made
<VirtualHost 192.168.1.52:443>
ServerName yourdomainname.com
DocumentRoot "/Library/Server/Web/Data/Sites/yourdomainname.com"
DirectoryIndex index.php index.html /wiki/ default.html
CustomLog /var/log/apache2/access_log combinedvhost
ErrorLog /var/log/apache2/error_log
<IfModule mod_ssl.c>
SSLEngine On
SSLCipherSuite "ALL:!aNULL:!ADH:!eNULL:!LOW:!EXP:RC4+RSA:+HIGH:+MEDIUM"
SSLProtocol -ALL +SSLv3 +TLSv1
SSLProxyEngine On
SSLCertificateFile "/etc/certificates/yourdomainname.com.E020BFD43F6E8E4786C035CCACE65D8E88B35496. cert.pem"
SSLCertificateKeyFile "/etc/certificates/yourdomainname.com.E020BFD43F6E8E4786C035CCACE65D8E88B35496. key.pem"
SSLCertificateChainFile "/etc/certificates/yourdomainname.com.E020BFD43F6E8E4786C035CCACE65D8E88B35496. chain.pem"
SSLProxyProtocol -ALL +SSLv3 +TLSv1
</IfModule>
<Directory "/Library/Server/Web/Data/Sites/yourdomainname.com">
Options All +MultiViews -ExecCGI -Indexes
AllowOverride None
<IfModule mod_dav.c>
DAV Off
</IfModule>
</Directory>
ServerAlias www.yourdomainname.com yourdomainname.biz www.yourdomainname.biz
Alias /phpMyAdmin /Library/Server/Web/Data/Sites/Default/p_admin/phpMyAdmin-3.5.2.2-english
</VirtualHost>
<VirtualHost 192.168.1.52:80>
ServerName yourdomainname.com
DocumentRoot "/Library/Server/Web/Data/Sites/yourdomainname.com"
DirectoryIndex index.php index.html /wiki/ default.html
CustomLog /var/log/apache2/access_log combinedvhost
ErrorLog /var/log/apache2/error_log
<IfModule mod_ssl.c>
SSLEngine Off
SSLCipherSuite "ALL:!aNULL:!ADH:!eNULL:!LOW:!EXP:RC4+RSA:+HIGH:+MEDIUM"
SSLProtocol -ALL +SSLv3 +TLSv1
SSLProxyEngine On
SSLProxyProtocol -ALL +SSLv3 +TLSv1
</IfModule>
<Directory "/Library/Server/Web/Data/Sites/yourdomainname.com">
Options All +MultiViews -ExecCGI -Indexes
AllowOverride None
<IfModule mod_dav.c>
DAV Off
</IfModule>
</Directory>
ServerAlias www.yourdomainname.com yourdomainname.biz www.yourdomainname.biz
</VirtualHost>
<Email Edited by Host>