Re: [w3c/browser-payment-api] How are digital signatures supported for Payment Requests? (#291)

> What's the motivation to sign the whole request and not just provide the signature in the payment method specific data?

Another way to phrase this question is "What is the information that needs to be digitally signed?"

The assertion is that there are some scenarios (like the ones mentioned above) where you'd want to digitally sign the payment items, the payment options, and the payment method data.

In the very least, we'll want to sign the payment method data. If that's the only requirement, then the solution is fairly easy. Unfortunately, that means that we definitely wouldn't be signing the payment details, which means none of the products or totals/discounts are digitally signed (which doesn't address a number of the use cases).

If we are able to sign everything (like  the WPCG spec supported), then we don't have to keep coming up with piece meal solutions every time we find out that we need to sign something else. The entire message is protected instead of developers having to understand what parts of the message are protected and what parts are not.

Again, I'm not taking a position on this. I'm just outlining the options available to us and noting that none of them seem to be easy decisions based on the series of design decisions that have gone into the Payment Request API.

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