feat(permit): initial flow

[alfetopito]

Summary

Initial implementation of the full flow for permittable tokens

PR will merge onto https://github.com/cowprotocol/cowswap/tree/hack/permit feature branch, safe to merge.

What is included

• Check token is permittable
  • For COW like tokens
  • On Goerli and Mainnet
• Cache the result permanently in localStorage
• Add pre-hook data to quote requests
  • If selected sell token is permittable, generates pre-hook and adds it to quote's request appData
  • This (and the permittable check) uses a fake PK to sign the request so users don't have to sign a msg just for quoting
• Request permit signature
  • When placing an order with a permittable token for the first time, the permit signature will be requested
  • Right now this signature is stored indefinitely in the browser
• Add pre-hook data to order
  • Once permit request is signed, the order will contain the pre-hook in its appData

TODOs

• More testing
• Continue refactoring
• Clear debug statements
• Test with different EOAs (hardware wallets)
• Address comments

What is NOT included

• Check token is permittable for DAI and USDC
• Check token is permittable on Gnosis Chain
• Detect when permit is expired/invalid
• Update the permit when expired/invalid
• Offer permit only when there's not enough allowance
• Additional UI changes being worked on by Michel

To Test

1. Connect on goerli with an EOA
2. Pick COW as the sell token (or UNI, also works)
3. Make sure to reset your allowance using for example revoke.cash
4. Pick a buy token
5. Check the quote requests in the console

• Should contain a hooks object withing the appData field as part of the request
• Note that not all requests contain this as they are for different reasons. Sasha is addressing that [2] feat: usd prices and amounts module #3081

6. Place the order

• There should be 1 signature requesting the allowance

7. Sign the permit signature

• There should be 1 signature for placing the order

8. Sign the request

• Order should be placed
• Order should be matched like usual

9. Once matched, check the approval for picked sell token on revoke.cash or similar

• Approval should be set to infinite