Think through how to support sending metadata / additional information alongside payments

[mistermoe]

Problem Statement

Providing additional information when sending money can often be quite helpful.

concrete examples that comes to mind are:

• can we think of a way for someone receiving a payment to know the sender's DAP instead of seeing a push notification that says "received x USDC from 0x2345676543234"
• Passing along a note or memo with a payment

I think it would be helpful if we could:

• come up with a handful of concrete use-cases aside from the ones mentioned above where inclusion of metadata would improve UX
• Weigh how important we feel supporting the use-cases we come up with is
• Brainstorm a handful of solutions to support said use-cases
• Decide on whether the solution should be a part of the DAP core spec or whether it should be considered as an auxiliary that can be used alongside DAPs

[!NOTE] My hunch is that figuring out how to pass along metadata will end up being quite important. The mechanism through which metadata is passed along would be built alongside or as something on top of DAPs themselves as potentially a separate standard. But maybe we can figure out a clean, simple, low-lift approach that fits in nicely as part of DAPs themselves

[geehsien]

In parallel with thinking about use cases, a few ways we can think about metadata broadly:

• Does the metadata need to be verified?
  • For simple memos like "Paying for pizza", there's nothing much to verify (i.e., what's the risk of a sender misrepresenting this?). But if it's a sender address (i.e. the sender's DAP), I'd think that should absolutely be verified in a trustless way. Something more in-between might be like an Order or Invoice ID.
• Is the metadata private?
  • The same way Venmo payments can be public/private, there almost certainly is the need for details to be kept private, whether it's the memo/details of the transaction, the sender's identity, or anything in between. Does there need to be some on-chain hash of the metadata, or can it exist entirely off-chain, as something the sender (their wallet, or the provider) can send to the receiving party's provider? E.g., does the serviceEndpoint need an additional endpoint where the sender can privately provide context/metadata to the receiver, in a verified/trusted way?