References:
https://www.tutorialspoint.com/php/php_login_example.htm
http://proquestcombo.safaribooksonline.com/book/programming/php/9781789535907/beginning-php/index_html?query=((php))#X2ludGVybmFsX0h0bWxWaWV3P3htbGlkPTk3ODE3ODk1MzU5MDclMkZjaDAybHZsMnNlYzIzX2h0bWwmcXVlcnk9KChwaHApKQ==