Update base64url library to match latest FCL lib

primitives/src/lib/Base64Url.sol

@@ -0,0 +1,76 @@
+// SPDX-License-Identifier: Apache-2.0
+pragma solidity ^0.8.0;
+
+/**
+ * @dev Encode (without '=' padding) 
+ * @author evmbrahmin, adapted from hiromin's Base64URL libraries
+ */
+library Base64Url {
+    /**
+     * @dev Base64Url Encoding Table
+     */
+    string internal constant ENCODING_TABLE =
+        "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_";
+
+    function encode(bytes memory data) internal pure returns (string memory) {
+        if (data.length == 0) return "";
+
+        // Load the table into memory
+        string memory table = ENCODING_TABLE;
+
+        string memory result = new string(4 * ((data.length + 2) / 3));
+
+        // @solidity memory-safe-assembly
+        assembly {
+            let tablePtr := add(table, 1)
+            let resultPtr := add(result, 32)
+
+            for {
+                let dataPtr := data
+                let endPtr := add(data, mload(data))
+            } lt(dataPtr, endPtr) {
+
+            } {
+                dataPtr := add(dataPtr, 3)
+                let input := mload(dataPtr)
+
+                mstore8(
+                    resultPtr,
+                    mload(add(tablePtr, and(shr(18, input), 0x3F)))
+                )
+                resultPtr := add(resultPtr, 1)
+
+                mstore8(
+                    resultPtr,
+                    mload(add(tablePtr, and(shr(12, input), 0x3F)))
+                )
+                resultPtr := add(resultPtr, 1)
+
+                mstore8(
+                    resultPtr,
+                    mload(add(tablePtr, and(shr(6, input), 0x3F)))
+                )
+                resultPtr := add(resultPtr, 1)
+
+                mstore8(resultPtr, mload(add(tablePtr, and(input, 0x3F))))
+                resultPtr := add(resultPtr, 1)
+            }
+
+            // Remove the padding adjustment logic
+            switch mod(mload(data), 3)
+            case 1 {
+                // Adjust for the last byte of data
+                resultPtr := sub(resultPtr, 2)
+            }
+            case 2 {
+                // Adjust for the last two bytes of data
+                resultPtr := sub(resultPtr, 1)
+            }
+
+            // Set the correct length of the result string
+            mstore(result, sub(resultPtr, add(result, 32)))
+        }
+
+        return result;  
+    }
+}

primitives/src/lib/FCL_Webauthn.sol

@@ -20,7 +20,7 @@
 // SPDX-License-Identifier: MIT
 pragma solidity ^0.8.12;
 
-import {Base64URL} from "./Base64URL.sol";
+import {Base64Url} from "./Base64Url.sol";
 import {FCL_Elliptic_ZZ} from "./FCL_elliptic.sol";
 
 library FCL_WebAuthn {
@@ -42,7 +42,8 @@ library FCL_WebAuthn {
                 revert InvalidAuthenticatorData();
             }
             // Verify that clientData commits to the expected client challenge
-            string memory challengeEncoded = Base64URL.encode32(abi.encodePacked(clientChallenge));
+            // Use the Base64Url encoding which omits padding characters to match WebAuthn Specification
+            string memory challengeEncoded = Base64Url.encode(abi.encodePacked(clientChallenge));
             bytes memory challengeExtracted = new bytes(
             bytes(challengeEncoded).length
         );
@@ -140,4 +141,4 @@ library FCL_WebAuthn {
 
         return result;
     }
-}
+}