Add custom derivation path support for QR flow

[evansmj]

Hi,

Casa.io is interested in adding more air gapped device support to its multisig vaults, including Jade. I know that via serial Jade supports exporting with custom derivation paths, but we are interested in adding support for Jade's QR flow.

The way Casa works is:

• Casa requests an xpub at m/45'.
• Casa's backend performs derivations for each vault+subaccount.

Are you open to a firmware update for Jade's QR flow that would allow users to export an xpub at m/45'?
(could be manually entered or they could select 'Casa multisig', some wallets such as Passport do this)

If so I could start working on a pr for it following your conventions and am open to your feedback.
Btw I've contributed to Blockstream on the Core Lightning side of things https://github.com/ElementsProject/cln-application/graphs/contributors?all=1.

[jgriffiths]

@bitcoinhelp FYI

[bitcoinhelp]

Hey @evansmj - yes adding this is something we've discussed quite a few times and willing to do it if any platforms needed this for QR support. I'd say we are open to manual entry or Casa preset (or both). Happy to review what you come up with if you already have a preferred UX

[evansmj]

@bitcoinhelp Thanks i'll get to work on it. I think a new preset where currently you select between "single sig" and "multisig" on the device will be the best UX. I'll explore how manual entry could work while I'm in there, seedsigner has this but its not great for regular users.

[bitcoinhelp]

@evansmj looking forward to it, note we can also add a 4th row on that screen to accommodate other ideas