Add Base64Url encoding (#4822)

Co-authored-by: Ernesto García <ernestognw@gmail.com>

test/utils/Base64.t.sol

@@ -0,0 +1,32 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.20;
+
+import {Test} from "forge-std/Test.sol";
+
+import {Base64} from "@openzeppelin/contracts/utils/Base64.sol";
+
+/// NOTE: This test requires `ffi` to be enabled. It does not run in the CI
+/// environment given `ffi` is not recommended.
+/// See: https://github.com/foundry-rs/foundry/issues/6744
+contract Base64Test is Test {
+    function testEncode(bytes memory input) external {
+        string memory output = Base64.encode(input);
+        assertEq(output, _base64Ffi(input, "encode"));
+    }
+
+    function testEncodeURL(bytes memory input) external {
+        string memory output = Base64.encodeURL(input);
+        assertEq(output, _base64Ffi(input, "encodeURL"));
+    }
+
+    function _base64Ffi(bytes memory input, string memory fn) internal returns (string memory) {
+        string[] memory command = new string[](4);
+        command[0] = "bash";
+        command[1] = "scripts/tests/base64.sh";
+        command[2] = fn;
+        command[3] = vm.toString(input);
+        bytes memory retData = vm.ffi(command);
+        return string(retData);
+    }
+}