Add whitelisting base files

contracts/WhiteListing/IKeyringChecker.sol

@@ -0,0 +1,15 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity =0.8.19;
+
+/// @title Keyring Checker Interface
+/// @notice Interface for a contract that checks credentials against a Keyring contract.
+interface IKeyringChecker {
+    /**
+     * @notice Checks if an entity has a valid credential and supports legacy interface.
+     * @param policyId The ID of the policy.
+     * @param entity The address of the entity to check.
+     * @return True if the entity has a valid credential, false otherwise.
+     */
+    function checkCredential(uint256 policyId, address entity) external view returns (bool);
+}

contracts/WhiteListing/mocks/MockedKeyringChecker.sol

@@ -0,0 +1,27 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity =0.8.19;
+
+import { IKeyringChecker } from "../interfaces/IKeyringChecker.sol";
+
+/// @title Mocked Keyring Checker
+/// @notice A mock implementation of IKeyringChecker for testing purposes
+contract MockedKeyringChecker is IKeyringChecker {
+    /// @notice Whether to allow the user or not.
+    bool public allow = false;
+
+    /// @notice Sets the allow flag.
+    /// @param _allow Whether to allow the user or not.
+    function setAllow(bool _allow) external {
+        allow = _allow;
+    }
+
+    /// @notice Checks if the user satisfies the policy.
+    /// @param policyId The policy ID to check against (unused in mock).
+    /// @param entity The address to check.
+    /// @return result True if the user satisfies the policy, false otherwise.
+    /* solhint-disable-next-line no-unused-vars */
+    function checkCredential(uint256 policyId, address entity) external view returns (bool) {
+        return allow;
+    }
+}