Protocol 19 - CAP-40 Signed Payload Signer

[sreuland]

have reviewed these changes for CAP-40 Signed Payload Signer on PR #413. renamed source repo branch to 'protocol-19', triggered 413 to close, opened this PR on new branch name.

Update the Java SDK to have the new XDR schema for Protocol 19

this change focuses on supporting CAP-40 , namely the new Signed Payload Signer as new StrKey.

Update the StrKey encoding/decoding to include the new Signed Payload Signer, add more tests where signed payload signer could appear such as SetOptionsOperation and AccountEntry.

Closes #412
Closes #410

can ignore all changed files in src/main/java/org/stellar/sdk/xdr, they are generated code from xdrgen tool against the latest xdr schema files.

This is first half of Protocol 19 support, a follow-on PR will be coming for remaining Protocol 19 support of CAP-21 which introduces new tx pre-conditions on of which is extraSigners which this new Signed Payload Signer can be used.

[leighmcculloch]

❓ Did we, or are we, adding a function for signing a payload and generating a decorated signature to attach to a transaction? I couldn't see that functionality in this PR.

[sreuland]

❓ Did we, or are we, adding a function for signing a payload and generating a decorated signature to attach to a transaction? I couldn't see that functionality in this PR.

Ok, have not done that aspect, just have the StrKey encode/decode updated for payload signer. Is that signature generation in the go client sdk for reference? I can get that in here. The encoded payload signer should go right into the Precondtions.ExtraSigners correct? And then I think need to add a AbstractTransaction.sign(SignedPayloadSigner signedPayloadSigner) to encapsulate both generation and adding the signedpayload decorated sig to the tx in one.

[leighmcculloch]

The signing operation should be independent of a transaction, then let people add the signature manually. That's how the Go SDK works anyway.

https://github.com/stellar/go/blob/horizon-protocol-19/keypair/full.go#L115-L123
https://github.com/stellar/go/blob/master/txnbuild/transaction.go#L332-L341

[sreuland]

The signing operation should be independent of a transaction, then let people add the signature manually. That's how the Go SDK works anyway.

@leighmcculloch , thanks for the references, I added similar convention into Java SDK, up for review on PR #415