public SslEngineFactory sslEngineFactory() {
        return sslEngineFactory;
    }
Returns host/IP address of remote host without reverse DNS lookup to be used as the host
for creating SSL engine. This is used as a hint for session reuse strategy and also for
hostname verification of server hostnames.
<p>
Scenarios:
<ul>
  <li>Server-side
  <ul>
    <li>Server accepts connection from a client. Server knows only client IP
    address. We want to avoid reverse DNS lookup of the client IP address since the server
    does not verify or use client hostname. The IP address can be used directly.</li>
  </ul>
  </li>
  <li>Client-side
  <ul>
    <li>Client connects to server using hostname. No lookup is necessary
    and the hostname should be used to create the SSL engine. This hostname is validated
    against the hostname in SubjectAltName (dns) or CommonName in the certificate if
    hostname verification is enabled. Authentication fails if hostname does not match.</li>
    <li>Client connects to server using IP address, but certificate contains only
    SubjectAltName (dns). Use of reverse DNS lookup to determine hostname introduces
    a security vulnerability since authentication would be reliant on a secure DNS.
    Hence hostname verification should fail in this case.</li>
    <li>Client connects to server using IP address and certificate contains
    SubjectAltName (ipaddress). This could be used when Kafka is on a private network.
    If reverse DNS lookup is used, authentication would succeed using IP address if lookup
    fails and IP address is used, but authentication would fail if lookup succeeds and
    dns name is used. For consistency and to avoid dependency on a potentially insecure
    DNS, reverse DNS lookup should be avoided and the IP address specified by the client for
    connection should be used to create the SSL engine.</li>
  </ul></li>
</ul>
clients/src/main/java/org/apache/kafka/common/security/ssl/SslFactory.java