Signing for Payment Zone microtransactions

[itamarro]

Since there's one bitcoin wallet for the Payment Zone, users all send their BTC to the same address (otherwise doing the settlement transactions would become costly).

Also, the CosmicBridge wallet doesn't integrate with Bitcoin directly - the user performs the payment via some other, standard bitcoin wallet.

This means the CosmicBridge wallet needs to know a user is actually the owner of a specific Bitcoin address like the user claims (otherwise the user could feed in any address and claim they're the owners of it). One easy way to do this is have the user sign a message one time via the private key. We can think of other ways too.

[lidarwin]

Changing the name because the method of using CosmicBridge/wallet (chrome extension) to sign a microtransaction is the best way.

To initiate a PZ Microtransaction, we must have the signature of the payer's bitcoin wallet. The functionality to sign something should be available in some form in the bcoin API.