OpenZeppelin Contracts v5.7 ships composable paymaster primitives, so sponsoring gas becomes a policy you write, not a bespoke contract.
The hard part in a paymaster is
validatePaymasterUserOp: you must decide who to sponsor and how to charge, then reconcile in postOp after the real gas cost is known. The new base contracts split this into pluggable checks: an ERC-20 paymaster pulls token payment at that price, a signature paymaster verifies an off-chain grant, an NFT-gated one checks ownership.Watch the postOp refund path: overcharge on validation, refund the delta after execution, or a reverting token transfer can grief the bundler. Test the
postOpReverted branch.OpenZeppelin Contracts v5.7
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