Auth via wallet signatures

All requests must be signed using eth_signTypedData_v4 with EIP-712 structured payloads.

Example signature payload:

{
  "domain": {
    "name": "Opus",
    "version": "1",
    "chainId": 1,
    "verifyingContract": "0xOpusAuth"
  },
  "message": {
    "wallet": "0xabc...",
    "action": "createTask"
  },
  "primaryType": "TaskAuthorization"
}