The solution looks good to me, but it needs one minor fix (see comment).

The underlying issue is here:

  public SSLEngine newSslEngine(AsyncHttpClientConfig config, String peerHost, int peerPort) {
    SSLEngine sslEngine =
      config.isDisableHttpsEndpointIdentificationAlgorithm() ?
        sslContext.newEngine(ByteBufAllocator.DEFAULT) :
        sslContext.newEngine(ByteBufAllocator.DEFAULT, domain(peerHost), peerPort);
    configureSslEngine(sslEngine, config);
    return sslEngine;
  }

https://github.com/AsyncHttpClient/async-http-client/blob/c959fa0483adb4a71fbccc5be94d8b6faa4f74be/client/src/main/java/org/asynchttpclient/netty/ssl/DefaultSslEngineFactory.java#L63-L70

Specifically, when the engine is created without the hostname, the engine does not have the hostname to then pass as a header, which breaks the SNI routing.

An alternative solution could have overridden the newSslEngine method, but that seems equivalent to this one, so no need to change this PR.

Additionally, I was concerned that this would affect the case where hostname verification is not enabled and SNI is not used, but I think we should be fine, since this is just a header and we pass these headers when creating the client ssl engines for the Pulsar Protocol connections.

Thanks for opening the PR @fantapsody, I didn't understand the issue originally, but the PR helped me see it.

LGTM

LGTM. Thanks @fantapsody!