♻️ Encode the challenge in base64 on-chain

src/WebAuthn.sol

@@ -1,14 +1,22 @@
 // SPDX-License-Identifier: MIT
 pragma solidity >=0.8.19 <0.9.0;
 
-// import { Base64 } from "../lib/solady/src/utils/Base64.sol";
+import { Base64 } from "../lib/solady/src/utils/Base64.sol";
 import { ECDSA256r1 } from "../lib/secp256r1-verify/src/ECDSA256r1.sol";
 
 error InvalidAuthenticatorData();
 error InvalidClientData();
 
-/// dev: this implementation assumes the caller check if User Presence (0x01) or User Verification (0x04) are set
+/// @title A library to verify ECDSA signature though WebAuthn on the secp256r1 curve
+/// @dev This implementation assumes the caller check if User Presence (0x01) or User Verification (0x04) are set
 library WebAuthn {
+    /// @notice Validate the webauthn data and generate the signature message needed to recover
+    /// @dev You may probably ask why we encode the challenge in base64 on-chain instead of
+    ///      of sending it already encoded to save some gas. This library is opiniated and
+    ///      it assumes that it is used in the context of Account Abstraction. In this context,
+    ///      valuable informations required to proceed the transaction will be stored in the challenge
+    ///      meaning we need the challenge in clear to use it later in the flow. That's why we decided to
+    ///      encode it here.
     function generateMessage(
         bytes1 authenticatorDataFlagMask,
         bytes calldata authenticatorData,
@@ -26,15 +34,15 @@ library WebAuthn {
                 revert InvalidAuthenticatorData();
             }
 
-            // TODO: Pass non-encode challenge? Convert the challenge to `bytes memory` and encode it to Base64
-            // bytes memory challengeEncoded = bytes(Base64.encode(abi.encodePacked(clientChallenge), true, true));
+            // Encode the client challenge in base64 and explicitly convert it to bytes
+            bytes memory challengeEncoded = bytes(Base64.encode(clientChallenge, true, true));
 
             // Extract the challenge from the client data and hash it
             bytes32 challengeHashed =
-                keccak256(clientData[clientChallengeOffset:(clientChallengeOffset + clientChallenge.length)]);
+                keccak256(clientData[clientChallengeOffset:(clientChallengeOffset + challengeEncoded.length)]);
 
-            // hash the encoded challenge and check both challenges are equal
-            if (keccak256(clientChallenge) != challengeHashed) {
+            // Hash the encoded challenge and check both challenges are equal
+            if (keccak256(challengeEncoded) != challengeHashed) {
                 revert InvalidClientData();
             }
 
@@ -43,6 +51,7 @@ library WebAuthn {
         }
     }
 
+    /// @notice Verify ECDSA signature though WebAuthn on the secp256r1 curve
     function verify(
         bytes1 authenticatorDataFlagMask,
         bytes calldata authenticatorData,
@@ -58,7 +67,6 @@ library WebAuthn {
         returns (bool)
     {
         unchecked {
-            // Verify the signature over sha256(authenticatorData || sha256(clientData))
             bytes32 message = generateMessage(
                 authenticatorDataFlagMask, authenticatorData, clientData, clientChallenge, clientChallengeOffset
             );

test/WebAuthn.t.sol

@@ -68,8 +68,8 @@ contract ContractTest is Test {
                 hex"65223a224e546f2d3161424547526e78786a6d6b61544865687972444e583369"
                 hex"7a6c7169316f776d4f643955474a30222c226f726967696e223a226874747073"
                 hex"3a2f2f66726573682e6c65646765722e636f6d222c2263726f73734f726967696e223a66616c73657d",
-                // clientChallengeBase64
-                hex"4e546f2d3161424547526e78786a6d6b61544865687972444e5833697a6c7169316f776d4f643955474a30",
+                // clientChallenge
+                hex"353a3ed5a0441919f1c639a46931de872ac3357de2ce5aa2d68c2639df54189d",
                 // clientChallengeOffset
                 0x24,
                 // r
@@ -95,8 +95,8 @@ contract ContractTest is Test {
             hex"65223a224e546f2d3161424547526e78786a6d6b61544865687972444e583369"
             hex"7a6c7169316f776d4f643955474a30222c226f726967696e223a226874747073"
             hex"3a2f2f66726573682e6c65646765722e636f6d222c2263726f73734f726967696e223a66616c73657d",
-            // clientChallengeBase64
-            hex"4e546f2d3161424547526e78786a6d6b61544865687972444e5833697a6c7169316f776d4f643955474a30",
+            // clientChallenge
+            hex"353a3ed5a0441919f1c639a46931de872ac3357de2ce5aa2d68c2639df54189d",
             // clientChallengeOffset
             0x24
         );