Async signer / verifier support

[Gozala]

@expede we've being trying to integrate rs-ucan into a system that need to make use of web crypto and ran up against sync API design

rs-ucan/ucan/src/did.rs

Lines 26 to 35 in c4d1cb7

	pub trait DidSigner {
	/// The associated DID type.
	type Did: Did + Clone;
	/// Get the associated DID.
	fn did(&self) -> &Self::Did;
	/// Get the associated signer instance.
	fn signer(&self) -> &<<Self::Did as Did>::VarsigConfig as Sign>::Signer;
	}

rs-ucan/varsig/src/signer.rs

Lines 11 to 40 in c4d1cb7

	pub trait Sign: Verify {
	/// The signing key.
	type Signer: Signer<Self::Signature>;
	/// Signing errors.
	type SignError: Error;
	/// Synchronously sign a payload.
	///
	/// # Errors
	///
	/// If encoding or signing fails, a `SignerError` is returned.
	#[allow(clippy::type_complexity)]
	#[tracing::instrument(skip_all)]
	fn try_sign<T, C: Codec<T>>(
	&self,
	codec: &C,
	signer: &Self::Signer,
	payload: &T,
	) -> Result<(Self::Signature, Vec<u8>), SignerError<C::EncodingError, Self::SignError>> {
	let mut buffer = Vec::new();
	codec
	.encode_payload(payload, &mut buffer)
	.map_err(SignerError::EncodingError)?;
	let sig = signer
	.try_sign(&buffer)
	.map_err(SignerError::SigningError)?;
	Ok((sig, buffer))
	}
	}

I do see there is also async Sign variant

rs-ucan/varsig/src/signer.rs

Line 43 in c4d1cb7

pub trait AsyncSign: Verify {

But as far as I can tell it isn't integrated anywhere and I'm not sure complexity of of having a sync / async split is worth it.

[expede]

Oh, yeah we can probably switch all of this to async and just turn most things into futures. A lot of in-memory signers in Rust are sync, and I've had to wrap them repeatedly at this point. There's an async-signer crate but I haven't gotten a lot of mileage out of it esp with Wasm.

Let's update that. It's probably a pretty mechanical change well suited to an LLM.

Anyhow, TL;DR: let's make this async everywhere and have the sync versions return a ready value. I can try to get to this later (in meetings all day) but also don't block on me

[Gozala]

Thanks for the response. We do have a fork where I did change things to async and integrated web crypto more tightly https://github.com/tonk-labs/rs-ucan/pulls we can try and integrate those changes back here if desired