mTLS（相互 TLS）

需要客户端证书进行身份验证：

# Server side
protocol:
  type: tls
  tls_targets:
    "example.com":
      cert: server.crt
      key: server.key
      client_ca_certs: [ca.crt]  # Required CA
      client_fingerprints: ["sha256:..."]  # Optional specific certs
      protocol: ...

# Client side
client_chain:
  address: "example.com:443"
  protocol:
    type: tls
    cert: client.crt
    key: client.key
    protocol: ...