Keysend

[kiwiidb]

Is your feature request related to a problem? Please describe.
Keysend is a way of sending spontaneous payments over Lightning, using just a public key, an amount and an optional memo as input.
Currently, the main use-case are "Value4Value" Podcasts, enable by podcasts apps like Breez, Fountain or Sphinx. An index of Value4Value podcasts can be found on Podcastindex.
However, there is no web-based value4value podcast player.

Describe the solution you'd like
Integrating keysend into Alby and into the webLN standard would allow for easy web-based value4value podcast players.
The keysend integration can be added to the following connectors:

• Alby wallet: lndhub.go now supports keysend, this is already live in the default Alby wallet in the extension.
• LND connector: for an example on how to do this, check out Blixt wallet.
• Eclair connector: API docs.
• LNBits connector: I don't think this is supported in the LNBits API, so this would not be possible (correct me if I'm wrong).
• Legacy LNDhub: not possible, but we probably would add the same endpoint as lndhub.go anyway, in case users want to connect to their own lndhub.go.

We would also need to extend the webLN spec to include support for keysend payments, so websites can integrate it.