Support personal_sign

[okwme]

Is your feature request related to a problem? Please describe.
My dapp among others utilize personal_sign as well as the older eth_sign and the newer varieties of eth_signTypedData to log users in. Gnosis safe could support this with the caveat that the app would need to realize the signature comes from a controlling key of the contract based wallet and not the wallet itself. With that additional information (maybe available via some other query?) safe users could log into dapps that utilize these sign in methods.

Describe the solution you'd like
Add support for eth_sign as well as optionally personal_sign and/or eth_signTypedData to be signed by controlling keys rather than included in the contract like described here: safe-global/safe-smart-account#127. Plus add another query that allows a dapp developer to check whether the web3 instance belongs to a contract based wallet or a pk based wallet.

This is a blocker for my dapp to support Gnosis Safe users. Furthermore I'm exploring a burner wallet onboarding flow where users are given Gnosis safes without realizing it. Should they wish to secure their accounts they will be able to instantiate the already created account within the safe app. This currently leads them to a dead end however, as once they use the safe, they would no longer be able to login to the dapp.

[okwme]

Relevant EIPs:

• ERC-1654 Dapp-wallet authentication process with contract wallets support ethereum/EIPs#1654
• ERC-1271 : Standard Signature Validation Method for Contracts  ethereum/EIPs#1271
• https://ethereum-magicians.org/t/erc-2126-signature-type-recognition/3392

[okwme]

And library for 1271 support:
https://www.npmjs.com/package/is-valid-signature