How to configure a Reactive WebClient to use 2-way TLS?

Question

I'm trying to configure a reactive WebClient to use 2-way TLS. I used this answer as a reference. (The one using a WebClientCustomizer, not the one using an InsecureTrustManager).

I double-checked the keystores and truststores on both client and server side, but the server sends back an error saying that the client is not presenting any certificate:

  @Bean
  WebClientCustomizer configureWebclient(@Value("${server.ssl.trust-store}") String trustStorePath, @Value("${server.ssl.trust-store-password}") String trustStorePass,
      @Value("${server.ssl.key-store}") String keyStorePath, @Value("${server.ssl.key-store-password}") String keyStorePass, @Value("${server.ssl.key-alias}") String keyAlias) {

    return new WebClientCustomizer() {

      @Override
      public void customize(Builder webClientBuilder) {
        SslContext sslContext;
        try {
          KeyStore trustStore = KeyStore.getInstance(KeyStore.getDefaultType());
          trustStore.load(new FileInputStream(ResourceUtils.getFile(trustStorePath)), trustStorePass.toCharArray());

          List<Certificate> certificateCollcetion = Collections.list(trustStore.aliases()).stream().filter(t -> {
            try {
              return trustStore.isCertificateEntry(t);
            } catch (KeyStoreException e1) {
              throw new RuntimeException("Error reading truststore", e1);
            }
          }).map(t -> {
            try {
              return trustStore.getCertificate(t);
            } catch (KeyStoreException e2) {
              throw new RuntimeException("Error reading truststore", e2);
            }
          }).collect(Collectors.toList());

          KeyStore keyStore = KeyStore.getInstance(KeyStore.getDefaultType());
          keyStore.load(new FileInputStream(ResourceUtils.getFile(keyStorePath)), keyStorePass.toCharArray());
          sslContext = SslContextBuilder.forClient()
              .keyManager((PrivateKey) keyStore.getKey(keyAlias, keyStorePass.toCharArray()))
              .trustManager((X509Certificate[]) certificateCollcetion.toArray(new X509Certificate[certificateCollcetion.size()]))
              .build();
        } catch (Exception e) {
          log.error("Error creating web client", e);
          throw new RuntimeException(e);
        }
        ClientHttpConnector connector = new ReactorClientHttpConnector((opt) -> {
          opt.sslContext(sslContext);
        });
        webClientBuilder.clientConnector(connector);
      }
    };
  }

Can somebody please share insight on how to correctly configure a reactive WebClient to use 2-way TLS?

Answer 1

For some reason the server would not accept the client certificate when the ssl context was built like this:

sslContext = SslContextBuilder.forClient()
          .keyManager((PrivateKey) keyStore.getKey(keyAlias, keyStorePass.toCharArray()))
          .trustManager((X509Certificate[]) certificateCollcetion.toArray(new X509Certificate[certificateCollcetion.size()]))
          .build();

To fix this, I had to initialize a KeyManagerFactory:

KeyManagerFactory keyManagerFactory = KeyManagerFactory.getInstance("SunX509");
keyManagerFactory.init(keyStore, keyStorePass.toCharArray());

Then I initialized the ssl context with the factory:

SslContext sslContext = SslContextBuilder.forClient()
                    .keyManager(keyManagerFactory)
                    .trustManager((X509Certificate[]) certificateCollection.toArray(new X509Certificate[certificateCollection.size()]))
                    .build();

After that, the server accepted the certificate and I could connect.

In summary, I used this cleaner solution that utilizes factories for both the key-store and the trust-store:

@Value("${server.ssl.trust-store}")
String trustStorePath;
@Value("${server.ssl.trust-store-password}")
String trustStorePass;
@Value("${server.ssl.key-store}")
String keyStorePath;
@Value("${server.ssl.key-store-password}")
String keyStorePass;

@Bean
public WebClient create2WayTLSWebClient() {

    ClientHttpConnector connector = new ReactorClientHttpConnector(
            options -> {
                options.option(ChannelOption.CONNECT_TIMEOUT_MILLIS, 5000);
                options.sslContext(get2WaySSLContext());
            }
    );

    return WebClient.builder()
            .clientConnector(connector)
            .build();

}

private SslContext get2WaySSLContext() {

    try {

        KeyStore keyStore = KeyStore.getInstance(KeyStore.getDefaultType());
        keyStore.load(new FileInputStream(ResourceUtils.getFile(keyStorePath)), keyStorePass.toCharArray());

        KeyManagerFactory keyManagerFactory = KeyManagerFactory.getInstance("SunX509");
        keyManagerFactory.init(keyStore, keyStorePass.toCharArray());

        KeyStore trustStore = KeyStore.getInstance(KeyStore.getDefaultType());
        trustStore.load(new FileInputStream(ResourceUtils.getFile(trustStorePath)), trustStorePass.toCharArray());

        TrustManagerFactory trustManagerFactory = TrustManagerFactory.getInstance("SunX509");
        trustManagerFactory.init(trustStore);

        return SslContextBuilder.forClient()
                .keyManager(keyManagerFactory)
                .trustManager(trustManagerFactory)
                .build();

    } catch (Exception e) {
        logger.error("Error creating 2-Way TLS WebClient. Check key-store and trust-store.");
        e.printStackTrace();
    }

    return null;
}

Just a note, if you are using Spring 5.1 or newer, this specific implementation will not work as you can no longer pass HttpClientOptions to a ReactorClientHttpConnector. Use this link as a guide for that configuration. However the meat of the code in this answer should still be applicable to that sort of configuration.