So, I added the next to my http.conf file:

Listen443

NameVirtualHost *:443

<VirtualHost *:443>
    DocumentRoot /PATH_TO/www
    ServerName www.domain.com
    SSLEngine on
    SSLCertificateFile /PATH_TO/domain.crt
    SSLCertificateKeyFile /PATH_TO/domain.key
    SSLCertificateChainFile /PATH_TO/intermediate.crt
</VirtualHost>

https://www.domain.com works now, however it shows the PHP source code? What could trigger this?

"Server configuration error" is the main reason -)

It's selecting for everyone PHP files as "plain content" rather than handing these to a PHP engine for processing. This does not have anything related to SSL (it'll just like happily send the "plain content" on the secure connection).

From PHP: Installation:

AddModule mod_php.c

LoadModule php_module         modules/mod_php.so

LoadModule php5_module        modules/libphp5.so

AddType application/x-httpd-php .php

And from PHP pages won't load:

AddType application/x-httpd-php .php

AddType application/x-httpd-php-source .phps

Visit a pattern? :-) Regardless, browse the fine installation instructions for the specific platform/server.

Happy coding.