Add Validation mechanism for SPSP

[AlexLakatos]

receipts_enabled
shared_secret
destination_account

From @marcoscaceres: Would be nice if the SPSP has an algorithm to hook directly into for validation. And it returned true or false. So... "perform simple payment validation", which takes a json object.

[sublimator]

Have been thinking along those lines myself.
But true/false seems less leaky than returning a balance (having said that you probably already know this anyway, from the receipt you have)

Would this require some kind of PKI ? The SPSP endpoint would need a lot more state.

With the current receipt model, backends integrating WM need to make requests to some receipt verifier upon each packet to "verify". So why not require a request to some SPSP endpoint?

[stale]

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[Starrcisco]

receipts_enabled shared_secret destination_account

From @marcoscaceres: Would be nice if the SPSP has an algorithm to hook directly into for validation. And it returned true or false. So... "perform simple payment validation", which takes a json object.

Please let me know