Another shameless plug - https://hashcash.io/ :)

homakov · on Dec 4, 2014

In your demo I'd be more careful with user input

>$url = 'https://hashcash.io/api/checkwork/' . $_REQUEST['hashcashid'] . '?apikey=[YOUR-PRIVATE-KEY]';

hashcashid can change URL completely to something like ../../newpath?newparams#

hippich · on Dec 4, 2014

it is always battle between make it simple to understand and bring best practices... in this particular case i chose simply to understand :)