Detecting if payment app is available

Hello WPWG members,

Following up on our discussion about this topic from f2f meeting.

I have prepared a problem statement and very early draft of proposals I had in mind on how merchants can securely check if a certain payment app is available.

You can find the document here,
https://github.com/maheshkk/webpayments/wiki/Detecting-if-payment-app-is-available

Please share if you have any questions or feedback! Also let me know if it is easier to discuss this by creating an issue in github and moving the content from wiki to this issue.

Thanks
Mahesh