Let buyers pay with arbitrary payment methods regardless of merchant support

[kumar303]

We discussed ways for merchants to introduce new payment providers to the user (issue #12) but such an ecosystem will be limited to providers that merchants choose to support.

Let's see what changes we'd need to make to the API to support a scenario where a user can pay with any arbitrary payment provider such as one the merchant does not yet support.

This would accomplish many things, such as:

• greater user choice in making payments
• more chances for innovative payment strategies to emerge (example: M-Pesa)
• equal market constraints for all parties in the transaction: buyers, merchants, and payment processors

There are many risks and challenges. Here is a brief summary:

• A merchant must be guaranteed to receive funds in the transaction
• A user must not be tricked into sending money to the wrong place (same challenge as issue Registering preferred payment providers #12)
• Standard phishing scenarios apply

[dlongley]

This issue is where the PaySwarm work comes in -- and should be leveraged. Any payment provider that is a PaySwarm Authority (supports the open PaySwarm protocol and is accepted as a valid authority by other PaySwarm Authorities/on the registered list) could be used by the customer to complete a purchase. The merchant could use any other PaySwarm Authority (or the same one) and could still transact with the customer.