Why is my PHP source code showing?

"Server configuration error" is the reason ;-)

It is choosing to serve PHP files as "plain content" instead of handing them to a PHP engine for processing. This doesn't have anything to do with SSL (it will just as happily send the "plain content" over a 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

See a pattern? :-) In any case, read the fine installation instructions for the particular platform/server.

Happy coding.

It could also be that your php.ini configuration is set to not parse code between short php tags.