Add Paymaster, PaymasterERC20, PaymasterERC20Guarantor, PaymasterERC721Owner and PaymasterSigner

.changeset/dark-papers-call.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': minor
+---
+
+`PaymasterERC721Owner`: Extension of `PaymasterCore` that approves sponsoring of user operation based on ownership of an ERC-721 NFT.

.changeset/polite-geckos-peel.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': minor
+---
+
+`PaymasterERC20`: Extension of `PaymasterCore` that sponsors user operations against payment in ERC-20 tokens.

.changeset/shy-poets-look.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': minor
+---
+
+`PaymasterSigner`: Extension of `PaymasterCore` that approves sponsoring of user operation based on a cryptographic signature verified by the paymaster.

.changeset/whole-items-rule.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': minor
+---
+
+`Paymaster`: Add a simple ERC-4337 paymaster implementation with minimal logic.

contracts/account/README.adoc

@@ -10,6 +10,11 @@ This directory includes contracts to build accounts for ERC-4337. These include:
  * {ERC7821}: Minimal batch executor implementation contracts. Useful to enable easy batch execution for smart contracts.
  * {ERC4337Utils}: Utility functions for working with ERC-4337 user operations.
  * {ERC7579Utils}: Utility functions for working with ERC-7579 modules and account modularity.
+ * {Paymaster}: An ERC-4337 paymaster implementation that includes the core logic to validate and pay for user operations.
+ * {PaymasterERC20}: A paymaster that allows users to pay for user operations using ERC-20 tokens.
+ * {PaymasterERC20Guarantor}: A paymaster that enables third parties to guarantee user operations by pre-funding gas costs, with the option for users to repay or for guarantors to absorb the cost.
+ * {PaymasterERC721Owner}: A paymaster that allows users to pay for user operations based on ERC-721 ownership.
+ * {PaymasterSigner}: A paymaster that allows users to pay for user operations using an authorized signature.
 
 == Core
 
@@ -23,6 +28,18 @@ This directory includes contracts to build accounts for ERC-4337. These include:
 
 {{ERC7821}}
 
+== Paymasters
+
+{{Paymaster}}
+
+{{PaymasterERC20}}
+
+{{PaymasterERC20Guarantor}}
+
+{{PaymasterERC721Owner}}
+
+{{PaymasterSigner}}
+
 == Utilities
 
 {{ERC4337Utils}}

contracts/account/paymaster/Paymaster.sol

@@ -0,0 +1,137 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.20;
+
+import {ERC4337Utils} from "../utils/draft-ERC4337Utils.sol";
+import {IEntryPoint, IPaymaster, PackedUserOperation} from "../../interfaces/draft-IERC4337.sol";
+
+/**
+ * @dev A simple ERC4337 paymaster implementation. This base implementation only includes the minimal logic to validate
+ * and pay for user operations.
+ *
+ * Developers must implement the {Paymaster-_validatePaymasterUserOp} function to define the paymaster's validation
+ * and payment logic. The `context` parameter is used to pass data between the validation and execution phases.
+ *
+ * The paymaster includes support to call the {IEntryPointStake} interface to manage the paymaster's deposits and stakes
+ * through the internal functions {deposit}, {withdraw}, {addStake}, {unlockStake} and {withdrawStake}.
+ *
+ * * Deposits are used to pay for user operations.
+ * * Stakes are used to guarantee the paymaster's reputation and obtain more flexibility in accessing storage.
+ *
+ * NOTE: See [Paymaster's unstaked reputation rules](https://eips.ethereum.org/EIPS/eip-7562#unstaked-paymasters-reputation-rules)
+ * for more details on the paymaster's storage access limitations.
+ */
+abstract contract Paymaster is IPaymaster {
+    /// @dev Unauthorized call to the paymaster.
+    error PaymasterUnauthorized(address sender);
+
+    /// @dev Revert if the caller is not the entry point.
+    modifier onlyEntryPoint() {
+        _checkEntryPoint();
+        _;
+    }
+
+    modifier onlyWithdrawer() {
+        _authorizeWithdraw();
+        _;
+    }
+
+    /// @dev Canonical entry point for the account that forwards and validates user operations.
+    function entryPoint() public view virtual returns (IEntryPoint) {
+        return ERC4337Utils.ENTRYPOINT_V09;
+    }
+
+    /// @inheritdoc IPaymaster
+    function validatePaymasterUserOp(
+        PackedUserOperation calldata userOp,
+        bytes32 userOpHash,
+        uint256 maxCost
+    ) public virtual onlyEntryPoint returns (bytes memory context, uint256 validationData) {
+        return _validatePaymasterUserOp(userOp, userOpHash, maxCost);
+    }
+
+    /// @inheritdoc IPaymaster
+    function postOp(
+        PostOpMode mode,
+        bytes calldata context,
+        uint256 actualGasCost,
+        uint256 actualUserOpFeePerGas
+    ) public virtual onlyEntryPoint {
+        _postOp(mode, context, actualGasCost, actualUserOpFeePerGas);
+    }
+
+    /**
+     * @dev Internal validation of whether the paymaster is willing to pay for the user operation.
+     * Returns the context to be passed to postOp and the validation data.
+     *
+     * The `requiredPreFund` is the amount the paymaster has to pay (in native tokens). It's calculated
+     * as `requiredGas * userOp.maxFeePerGas`, where `required` gas can be calculated from the user operation
+     * as `verificationGasLimit + callGasLimit + paymasterVerificationGasLimit + paymasterPostOpGasLimit + preVerificationGas`
+     */
+    function _validatePaymasterUserOp(
+        PackedUserOperation calldata userOp,
+        bytes32 userOpHash,
+        uint256 requiredPreFund
+    ) internal virtual returns (bytes memory context, uint256 validationData);
+
+    /**
+     * @dev Handles post user operation execution logic. The caller must be the entry point.
+     *
+     * It receives the `context` returned by `_validatePaymasterUserOp`. Function is not called if no context
+     * is returned by {validatePaymasterUserOp}.
+     *
+     * NOTE: The `actualUserOpFeePerGas` is not `tx.gasprice`. A user operation can be bundled with other transactions
+     * making the gas price of the user operation to differ.
+     */
+    function _postOp(
+        PostOpMode /* mode */,
+        bytes calldata /* context */,
+        uint256 /* actualGasCost */,
+        uint256 /* actualUserOpFeePerGas */
+    ) internal virtual {}
+
+    /// @dev Calls {IEntryPointStake-depositTo}.
+    function deposit() public payable virtual {
+        entryPoint().depositTo{value: msg.value}(address(this));
+    }
+
+    /// @dev Calls {IEntryPointStake-withdrawTo}.
+    function withdraw(address payable to, uint256 value) public virtual onlyWithdrawer {
+        entryPoint().withdrawTo(to, value);
+    }
+
+    /// @dev Calls {IEntryPointStake-addStake}.
+    function addStake(uint32 unstakeDelaySec) public payable virtual {
+        entryPoint().addStake{value: msg.value}(unstakeDelaySec);
+    }
+
+    /// @dev Calls {IEntryPointStake-unlockStake}.
+    function unlockStake() public virtual onlyWithdrawer {
+        entryPoint().unlockStake();
+    }
+
+    /// @dev Calls {IEntryPointStake-withdrawStake}.
+    function withdrawStake(address payable to) public virtual onlyWithdrawer {
+        entryPoint().withdrawStake(to);
+    }
+
+    /// @dev Ensures the caller is the {entrypoint}.
+    function _checkEntryPoint() internal view virtual {
+        address sender = msg.sender;
+        if (sender != address(entryPoint())) {
+            revert PaymasterUnauthorized(sender);
+        }
+    }
+
+    /**
+     * @dev Checks whether `msg.sender` withdraw funds stake or deposit from the entrypoint on paymaster's behalf.
+     *
+     * Use of an xref:api:access.adoc[access control]
+     * modifier such as {Ownable-onlyOwner} is recommended.
+     *
+     * ```solidity
+     * function _authorizeUpgrade() internal onlyOwner {}
+     * ```
+     */
+    function _authorizeWithdraw() internal virtual;
+}