## 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.
