Accept Auth Address signatures for Account Associations

[deodad]

We can improve the developer experience for building Mini Apps by allowing the Account Association to be signed by an Auth Address. This will enable developers to generate these signatures on web in the Farcaster app where their development is happening. It will also allow other clients to support generating these signatures.

Developers
No change is required.

Farcaster Clients or anyone validating account associations
Accept Json Farcaster Signature of key type auth in addition to custody. We recently published @farcaster/jfs to make verifying signatures easier. Note that this verifies the signature but consumers must still validate the key used to sign is registered with the FID and active.

This was implemented by Farcaster and Neynar mid-June.

[PirosB3]

This is complete, Auth Addresses can be used to sign Account Associations