feat(contracts): Implement a default withdraw function

contracts/src/DefaultPortal.sol

@@ -17,7 +17,4 @@ contract DefaultPortal is AbstractPortal {
    * @dev This sets the addresses for the AttestationRegistry, ModuleRegistry and PortalRegistry
    */
   constructor(address[] memory modules, address router) AbstractPortal(modules, router) {}
-
-  /// @inheritdoc AbstractPortal
-  function withdraw(address payable to, uint256 amount) external override {}
 }

contracts/src/abstracts/AbstractPortal.sol

@@ -27,6 +27,9 @@ abstract contract AbstractPortal is IPortal {
   /// @notice Error thrown when someone else than the portal's owner is trying to revoke
   error OnlyPortalOwner();
 
+  /// @notice Error thrown when withdrawing funds fails
+  error WithdrawFail();
+
   /**
    * @notice Contract constructor
    * @param _modules list of modules to use for the portal (can be empty)
@@ -42,12 +45,16 @@ abstract contract AbstractPortal is IPortal {
   }
 
   /**
-   * @notice Optional method to withdraw funds from the Portal
+   * @notice Withdraw funds from the Portal
    * @param to the address to send the funds to
    * @param amount the amount to withdraw
-   * @dev DISCLAIMER: by default, this method is not implemented and should be overridden if funds are to be withdrawn
+   * @dev Only the Portal owner can withdraw funds
    */
-  function withdraw(address payable to, uint256 amount) external virtual;
+  function withdraw(address payable to, uint256 amount) external virtual {
+    if (msg.sender != portalRegistry.getPortalByAddress(address(this)).ownerAddress) revert OnlyPortalOwner();
+    (bool s, ) = to.call{ value: amount }("");
+    if (!s) revert WithdrawFail();
+  }
 
   /**
    * @notice Attest the schema with given attestationPayload and validationPayload

contracts/test/DefaultPortal.t.sol

@@ -21,6 +21,7 @@ contract DefaultPortalTest is Test {
   AttestationRegistryMock public attestationRegistryMock = new AttestationRegistryMock();
   Router public router = new Router();
   address public portalOwner = makeAddr("portalOwner");
+  address public recipient = makeAddr("recipient");
 
   event Initialized(uint8 version);
   event PortalRegistered(string name, string description, address portalAddress);
@@ -328,4 +329,41 @@ contract DefaultPortalTest is Test {
     bool isAbstractPortalSupported = defaultPortal.supportsInterface(type(AbstractPortal).interfaceId);
     assertEq(isAbstractPortalSupported, true);
   }
+
+  function test_withdraw_byOwner() public {
+    // Fund the portal contract with 1 ether
+    vm.deal(address(defaultPortal), 1 ether);
+
+    // Set the amount to withdraw
+    uint256 withdrawAmount = 0.5 ether;
+    uint256 recipientInitialBalance = recipient.balance;
+
+    // Attempt withdrawal by the owner
+    vm.prank(portalOwner);
+    defaultPortal.withdraw(payable(recipient), withdrawAmount);
+
+    // Verify the recipient's balance has increased by the withdrawal amount
+    assertEq(recipient.balance, recipientInitialBalance + withdrawAmount);
+  }
+
+  function test_withdrawFail_OnlyPortalOwner() public {
+    // Attempt withdrawal by a non-owner address
+    uint256 withdrawAmount = 0.5 ether;
+    vm.prank(makeAddr("nonOwner"));
+    vm.expectRevert(AbstractPortal.OnlyPortalOwner.selector);
+
+    defaultPortal.withdraw(payable(recipient), withdrawAmount);
+  }
+
+  function test_withdrawFail_InsufficientBalance() public {
+    // Fund the portal contract with less than the requested amount
+    vm.deal(address(defaultPortal), 0.25 ether);
+
+    // Attempt withdrawal of 0.5 ether
+    uint256 withdrawAmount = 0.5 ether;
+    vm.prank(portalOwner);
+    vm.expectRevert(AbstractPortal.WithdrawFail.selector);
+
+    defaultPortal.withdraw(payable(recipient), withdrawAmount);
+  }
 }