Let the user sign an arbitrary message with its keystore

[Marketen]

Currently, web3signer only permits signing certain types of data (as body payloads) in the /api/v1/eth2/sign/{identifier} ETH2 endpoint or /api/v1/eth1/sign/{identifier} ETH1 endpoint. See https://consensys.github.io/web3signer/web3signer-eth2.html

It would be nice to add an endpoint (probably in ETH2 mode or both ETH1 & ETH2) that signs an arbitrary payload sent by the user. Something like:

"message": {
    "platform": "dappnode",
    "timestamp": "185921877",
    "pubkey":
    "0xaf294f5663defdba078e0c16b349952ab762f8019f42f45fc0a369666e12d836247e4d7a3e3bd564826dcffcfdc50114"
},

This is outside web3signer main scope, it would let users sign messages not necessarily related to the eth2 protocol

[pablomendezroyo]

To follow best practices and let others benefit from this approach and not only dappnode, how feasible would it be to add to the standard a new type of signing to the existing endpoint /api/v1/eth2/sign/{identifier} to proof validation? something like "type": "PROOF_OF_VALIDATION":

Request:

{
  "type": "PROOF_OF_VALIDATION",
  "platform": "",
  "timestamp": "",
  "pubkey": "",
}

Edit: the pubkey might be omitted in the request as long as it is included as the identifier when doing the request

Response:

  "message": {
    "platform": "",
    "timestamp": "",
    "pubkey": "",
  },
  "signature": ""

[usmansaleem]

@pablomendezroyo It is do-able as we already have DEPOSIT and VALIDATOR_REGISTRATION which doesn't take fork_info as input parameter. The only thing to work out is that all other types attach a "domain" when calculating the signing root. I am assuming this one would be a simple signing?

[pablomendezroyo]

@usmansaleem you right, it would be a simple signing