[LSP9] Should we add ERC1271 to verify signatures at the vault

[frozeman]

Adding ERC1271 isValidSignature() to an LSP9 vault would allow for login with a vault. Then vault would then call the isValidSignature() on the owner, to see if the signature can be verified by one of the SIGN keys controlling the UP/ower contract.

currently LSP9 does not have ERC1271, as any app can always detect the owner and call isValidSignature() on the owner himself.

[DanielAbalde]

We can't call isValidSignature() from an EOA, so adding ERC1271 depends on whether you want an EOA to be able to sign on an LSP9, right? If this is the case, I think it is good to add it and that the Lukso ecosystem is not closed to UP however better it is.