SEP-10 v3.0 Changes (from the SDF)

sep10-v3.0.0-change

## SEP-10 3.0

### TL;DR

Implement the changes described in the [SEP-10 v3.0 PR](https://github.com/stellar/stellar-protocol/pull/746) by November 13th. It adds a check for the correct `homeDomain` value in the SEP-10 challenge transaction. `homeDomain` is the domain hosting the [SEP-1 stellar.toml](sep-0001.md) containing a `WEB_AUTH_ENDPOINT` and `SIGNING_KEY`.

The SEP-10 v3.0 PR is not merged, but the only changes still in discussion relate to phrasing. No more functional changes will be introduced.

### Background & Description

Thank you for implementing SEP-10 v2.1, this removed the possibility of unexpected SEP-10 client-anchor incompatibility. Now that Anchors have been given time to update, Wallets can soon expect the Anchors they interact with to have a v2.1 challenge. This means their challenge transactions include the home domain that hosts the [SEP-1 stellar.toml](https://github.com/stellar/stellar-protocol/blob/master/ecosystem/sep-0001.md) that has the `WEB_AUTH_ENDPOINT` used to obtain the JWT.

The next step is for SDK's to release changes supporting SEP-10 v3.0, which adds the check for the expected `homeDomain` back to SEP-10. **Wallets should upgrade only when their partner anchors have upgraded to v2.1**. This should be the case for all anchors by the time your v3.0 change is released.

### Deadline

The SDF asks all SDK's to release new versions including SEP-10 v3.0 support by **November 13th**. On Monday November 16th the SDF will announce to the ecosystem SDK support for SEP-10 v3.0.