SatoshiPortal
Endpoint and scripts for PSBT
Once Bitcoin Core 0.17 comes out, we can create PSBT files using the standard in Bitcoin Core.
I think the best way to do this is to get people to add trasnsactions to a batch first via "addtobatch" and then create a PSBT file from a batch, since we already have all the UTXOs and amounts for that batch. This allows us to manage different batches of transactions.
The app would then select which batch it wants to create as a PSBT file, proxy would dispatch to Bitcoin Core to create the PSBT file and return it to the proxy which sends it to the app.
The app then returns a signed PSBT file to the proxy, which sends it to Bitcoin Core for broadcast.
Update: still pending. Work on this can be still done even before we have the user interface and coldcard plugin