How to create login and interaction between web and smartphone using ajax etc

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Ajax

database

HTML5

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I liked the Whatsapp Web feature to login using QR code, which is scanned by smartphone(tested on Android). So I wanted to make a website which uses smartphone as a login tool and as well as interaction tool. For example like a remote. To be very clear I dont want to use any screencasting tools or tools like teamviewer etc.

I came across this website which exactly reflects the way I wish to use my website in combination of my smartphone.

Here is the link : http://20.okeanelzy.com/en/

Use this link see what I mean.

I tried the web but this is the best that I got:https://github.com/zxing/zxing/wiki/Scanning-From-Web-Pages

But still dont know how to connect smartphone and website.

Maybe using Ajax or db? whatsoever kindly help me out. Thanks a lot.