• No external HTTP resources required (see https://github.com/geir54/php-sqrl/blob/0fa574520a1843a33a84c3985f934e84af6f2042/sqrl_verify.php for an example of what we WON'T do)
• Support PECL Sodium if it exists
  • If it doesn't polyfill this with a pure-PHP implementation a'la https://github.com/devi/Salt
• Find a good QR library; if one doesn't exist, we'll have to write one
• PSR compliance (the specific PSR is open to discussion; this library should be usable with any popular framework: CodeIgniter, Cake, Zend, Laravel, Symfony2, Yii, etc.)

https://www.grc.com/sqrl/sqrl.htm