EIP 712 authorizations

[wjmelements]

We would like to be able to authorize a session key without signing a transaction.

[wjmelements]

One benefit of this is that such an authorization would be very easy to verify off-chain.

[wjmelements]

We could consider changing the address signer into a full public key

[wjmelements]

full public key
easy to verify off-chain

Would also want to support other public keys so the registry can be used for things like bls signatures. Because these public keys can have different lengths, perhaps the longer ones should be hashed.

[wjmelements]

While this registry only needs to support address, I want for the signature to also be useful for authorization offchain. EIP-712 has domainSeparator which includes address(this). Perhaps the authorization can ignore the domainSeparator.