Use [u8; 32] rather than Hmac<Sha256> for simplicity

Mapping an `Hmac<Sha256>` would require somewhat custom logic as
we'd have to behave differently based on generic parameters, so its
simplest to just swap it to a `[u8; 32]` instead.

Author: TheBlueMatt

lightning/src/blinded_path/payment.rs

@@ -332,7 +332,7 @@ pub struct ReceiveTlvs {
 	/// The TLVs for which the HMAC in `authentication` is derived.
 	pub(crate) tlvs: UnauthenticatedReceiveTlvs,
 	/// An HMAC of `tlvs` along with a nonce used to construct it.
-	pub(crate) authentication: (Hmac<Sha256>, Nonce),
+	pub(crate) authentication: ([u8; 32], Nonce),
 }
 
 impl ReceiveTlvs {

lightning/src/ln/channelmanager.rs

@@ -570,24 +570,25 @@ pub trait Verification {
 	/// [`Nonce`].
 	fn hmac_for_offer_payment(
 		&self, nonce: Nonce, expanded_key: &inbound_payment::ExpandedKey,
-	) -> Hmac<Sha256>;
+	) -> [u8; 32];
 
 	/// Authenticates the data using an HMAC and a [`Nonce`] taken from an [`OffersContext`].
 	fn verify_for_offer_payment(
-		&self, hmac: Hmac<Sha256>, nonce: Nonce, expanded_key: &inbound_payment::ExpandedKey,
+		&self, hmac: [u8; 32], nonce: Nonce, expanded_key: &inbound_payment::ExpandedKey,
 	) -> Result<(), ()>;
 }
 
 impl Verification for UnauthenticatedReceiveTlvs {
 	fn hmac_for_offer_payment(
 		&self, nonce: Nonce, expanded_key: &inbound_payment::ExpandedKey,
-	) -> Hmac<Sha256> {
-		signer::hmac_for_payment_tlvs(self, nonce, expanded_key)
+	) -> [u8; 32] {
+		signer::hmac_for_payment_tlvs(self, nonce, expanded_key).to_byte_array()
 	}
 
 	fn verify_for_offer_payment(
-		&self, hmac: Hmac<Sha256>, nonce: Nonce, expanded_key: &inbound_payment::ExpandedKey,
+		&self, hmac: [u8; 32], nonce: Nonce, expanded_key: &inbound_payment::ExpandedKey,
 	) -> Result<(), ()> {
+		let hmac = bitcoin::hashes::hmac::Hmac::from_byte_array(hmac);
 		signer::verify_payment_tlvs(self, hmac, nonce, expanded_key)
 	}
 }