Overview

Permit2 is a unification of 2 contracts, SignatureTransfer and AllowanceTransfer. The SignatureTransfer contract handles all signature-based transfers, meaning that an allowance on the token is bypassed and permissions to the spender only last for the duration of the transaction that the one-time signature is spent. The AllowanceTransfer contract handles setting allowances on tokens, giving permissions to spenders on a specified amount for a specified duration of time. Any transfers that then happen through the AllowanceTransfer contract will only succeed if the proper permissions have been set.

Resources

A great explanation of the Permit2 contract and example usage.

Approving Permit2

Before integrating contracts can request users’ tokens through Permit2, users must approve the Permit2 contract through the specific token contract by calling something like:

USDC.approve(permit2Address, totalAmount);

To get the maximal benefits from Permit2, users should do a max approval on the contract where:

totalAmount = type(uint256).max;