SEP-10 v3.1 Changes (from the SDF)

[JakeUrban]

SEP-10 3.1 Support

TL;DR

Implement the changes described the SEP-10 3.1 commit.

This likely involves adding an optional argument to the SEP-10 utility functions for adding an additional Manage Data operation containing the domain of the SEP-10 server (web_auth_domain).

Background & Description

Thank you for implementing SEP-10 v3.0, which reintroduced verification of the home domain of the service requiring SEP-10 authentication, ensuring that signed challenges cannot be used for any other service.

SEP-10 v3.1 adds an optional Manage Data operation that includes the home domain of the service issuing SEP-10 challenges. This allows clients and servers to verify the issuer of the challenge.

[JakeUrban]

stellar/stellar-protocol#767