Peter Davies 807283538f Add client authentication to Web3Signer validators (#3170 )

## Issue Addressed

Web3Signer validators do not support client authentication. This means the `--tls-known-clients-file` option on Web3Signer can't be used with Lighthouse.

## Proposed Changes

Add two new fields to Web3Signer validators, `client_identity_path` and `client_identity_password`, which specify the path and password for a PKCS12 file containing a certificate and private key. If `client_identity_path` is present, use the certificate for SSL client authentication.

## Additional Info

I am successfully validating on Prater using client authentication with Web3Signer and client authentication.

2022-05-18 23:14:37 +00:00

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Remote Signing with Web3Signer

Web3Signer is a tool by Consensys which allows remote signing. Remote signing is when a Validator Client (VC) out-sources the signing of messages to remote server (e.g., via HTTPS). This means that the VC does not hold the validator private keys.

Warnings

Using a remote signer comes with risks, please read the following two warnings before proceeding:

Remote signing is complex and risky

Remote signing is generally only desirable for enterprise users or users with unique security requirements. Most users will find the separation between the Beacon Node (BN) and VC to be sufficient without introducing a remote signer.

Using a remote signer introduces a new set of security and slashing risks and should only be undertaken by advanced users who fully understand the risks.

Web3Signer is not maintained by Lighthouse

The Web3Signer tool is maintained by Consensys, the same team that maintains Teku. The Lighthouse team (Sigma Prime) does not maintain Web3Signer or make any guarantees about its safety or effectiveness.

Usage

A remote signing validator is added to Lighthouse in much the same way as one that uses a local keystore, via the validator_definitions.yml file or via the POST /lighthouse/validators/web3signer API endpoint.

Here is an example of a validator_definitions.yml file containing one validator which uses a remote signer:

---
- enabled: true
  voting_public_key: "0xa5566f9ec3c6e1fdf362634ebec9ef7aceb0e460e5079714808388e5d48f4ae1e12897fed1bea951c17fa389d511e477"
  type: web3signer
  url: "https://my-remote-signer.com:1234"
  root_certificate_path: /home/paul/my-certificates/my-remote-signer.pem
  client_identity_path: /home/paul/my-keys/my-identity-certificate.p12
  client_identity_password: "password"

When using this file, the Lighthouse VC will perform duties for the 0xa5566.. validator and defer to the https://my-remote-signer.com:1234 server to obtain any signatures. It will load a "self-signed" SSL certificate from /home/paul/my-certificates/my-remote-signer.pem (on the filesystem of the VC) to encrypt the communications between the VC and Web3Signer. It will use SSL client authentication with the "self-signed" certificate in /home/paul/my-keys/my-identity-certificate.p12.

The request_timeout_ms key can also be specified. Use this key to override the default timeout with a new timeout in milliseconds. This is the timeout before requests to Web3Signer are considered to be failures. Setting a value that is too long may create contention and late duties in the VC. Setting it too short will result in failed signatures and therefore missed duties.

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