Java HTTPS client certificate authentication

Question

Finally managed to solve all the issues, so I'll answer my own question. These are the settings/files I've used to manage to get my particular problem(s) solved;

The client's keystore is a PKCS#12 format file containing

1. The client's public certificate (in this instance signed by a self-signed CA)
2. The client's private key

To generate it I used OpenSSL's pkcs12 command, for example;

openssl pkcs12 -export -in client.crt -inkey client.key -out client.p12 -name "Whatever"

Tip: make sure you get the latest OpenSSL, not version 0.9.8h because that seems to suffer from a bug which doesn't allow you to properly generate PKCS#12 files.

This PKCS#12 file will be used by the Java client to present the client certificate to the server when the server has explicitly requested the client to authenticate. See the Wikipedia article on TLS for an overview of how the protocol for client certificate authentication actually works (also explains why we need the client's private key here).

The client's truststore is a straight forward JKS format file containing the root or intermediate CA certificates. These CA certificates will determine which endpoints you will be allowed to communicate with, in this case it will allow your client to connect to whichever server presents a certificate which was signed by one of the truststore's CA's.

To generate it you can use the standard Java keytool, for example;

keytool -genkey -dname "cn=CLIENT" -alias truststorekey -keyalg RSA -keystore ./client-truststore.jks -keypass whatever -storepass whatever
keytool -import -keystore ./client-truststore.jks -file myca.crt -alias myca

Using this truststore, your client will try to do a complete SSL handshake with all servers who present a certificate signed by the CA identified by myca.crt.

The files above are strictly for the client only. When you want to set-up a server as well, the server needs its own key- and truststore files. A great walk-through for setting up a fully working example for both a Java client and server (using Tomcat) can be found on this website.

Issues/Remarks/Tips

1. Client certificate authentication can only be enforced by the server.
2. (Important!) When the server requests a client certificate (as part of the TLS handshake), it will also provide a list of trusted CA's as part of the certificate request. When the client certificate you wish to present for authentication is not signed by one of these CA's, it won't be presented at all (in my opinion, this is weird behaviour, but I'm sure there's a reason for it). This was the main cause of my issues, as the other party had not configured their server properly to accept my self-signed client certificate and we assumed that the problem was at my end for not properly providing the client certificate in the request.
3. Get Wireshark. It has great SSL/HTTPS packet analysis and will be a tremendous help debugging and finding the problem. It's similar to -Djavax.net.debug=ssl but is more structured and (arguably) easier to interpret if you're uncomfortable with the Java SSL debug output.

4. It's perfectly possible to use the Apache httpclient library. If you want to use httpclient, just replace the destination URL with the HTTPS equivalent and add the following JVM arguments (which are the same for any other client, regardless of the library you want to use to send/receive data over HTTP/HTTPS):

   -Djavax.net.debug=ssl
   -Djavax.net.ssl.keyStoreType=pkcs12
   -Djavax.net.ssl.keyStore=client.p12
   -Djavax.net.ssl.keyStorePassword=whatever
   -Djavax.net.ssl.trustStoreType=jks
   -Djavax.net.ssl.trustStore=client-truststore.jks
   -Djavax.net.ssl.trustStorePassword=whatever

Other answers show how to globally configure client certificates. However if you want to programmatically define the client key for one particular connection, rather than globally define it across every application running on your JVM, then you can configure your own SSLContext like so:

String keyPassphrase = "";

KeyStore keyStore = KeyStore.getInstance("PKCS12");
keyStore.load(new FileInputStream("cert-key-pair.pfx"), keyPassphrase.toCharArray());

SSLContext sslContext = SSLContexts.custom()
        .loadKeyMaterial(keyStore, null)
        .build();

HttpClient httpClient = HttpClients.custom().setSSLContext(sslContext).build();
HttpResponse response = httpClient.execute(new HttpGet("https://example.com"));

They JKS file is just a container for certificates and key pairs. In a client-side authentication scenario, the various parts of the keys will be located here:

• The client's store will contain the client's private and public key pair. It is called a keystore.
• The server's store will contain the client's public key. It is called a truststore.

The separation of truststore and keystore is not mandatory but recommended. They can be the same physical file.

To set the filesystem locations of the two stores, use the following system properties:

-Djavax.net.ssl.keyStore=clientsidestore.jks

and on the server:

-Djavax.net.ssl.trustStore=serversidestore.jks

To export the client's certificate (public key) to a file, so you can copy it to the server, use

keytool -export -alias MYKEY -file publicclientkey.cer -store clientsidestore.jks

To import the client's public key into the server's keystore, use (as the the poster mentioned, this has already been done by the server admins)

keytool -import -file publicclientkey.cer -store serversidestore.jks

Maven pom.xml:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>some.examples</groupId>
    <artifactId>sslcliauth</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>jar</packaging>
    <name>sslcliauth</name>
    <dependencies>
        <dependency>
            <groupId>org.apache.httpcomponents</groupId>
            <artifactId>httpclient</artifactId>
            <version>4.4</version>
        </dependency>
    </dependencies>
</project>

Java code:

package some.examples;

import java.io.FileInputStream;
import java.io.IOException;
import java.security.KeyManagementException;
import java.security.KeyStore;
import java.security.KeyStoreException;
import java.security.NoSuchAlgorithmException;
import java.security.UnrecoverableKeyException;
import java.security.cert.CertificateException;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.net.ssl.SSLContext;
import org.apache.http.HttpEntity;
import org.apache.http.HttpHost;
import org.apache.http.client.config.RequestConfig;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.conn.ssl.SSLConnectionSocketFactory;
import org.apache.http.ssl.SSLContexts;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;
import org.apache.http.entity.InputStreamEntity;

public class SSLCliAuthExample {

private static final Logger LOG = Logger.getLogger(SSLCliAuthExample.class.getName());

private static final String CA_KEYSTORE_TYPE = KeyStore.getDefaultType(); //"JKS";
private static final String CA_KEYSTORE_PATH = "./cacert.jks";
private static final String CA_KEYSTORE_PASS = "changeit";

private static final String CLIENT_KEYSTORE_TYPE = "PKCS12";
private static final String CLIENT_KEYSTORE_PATH = "./client.p12";
private static final String CLIENT_KEYSTORE_PASS = "changeit";

public static void main(String[] args) throws Exception {
    requestTimestamp();
}

public final static void requestTimestamp() throws Exception {
    SSLConnectionSocketFactory csf = new SSLConnectionSocketFactory(
            createSslCustomContext(),
            new String[]{"TLSv1"}, // Allow TLSv1 protocol only
            null,
            SSLConnectionSocketFactory.getDefaultHostnameVerifier());
    try (CloseableHttpClient httpclient = HttpClients.custom().setSSLSocketFactory(csf).build()) {
        HttpPost req = new HttpPost("https://changeit.com/changeit");
        req.setConfig(configureRequest());
        HttpEntity ent = new InputStreamEntity(new FileInputStream("./bytes.bin"));
        req.setEntity(ent);
        try (CloseableHttpResponse response = httpclient.execute(req)) {
            HttpEntity entity = response.getEntity();
            LOG.log(Level.INFO, "*** Reponse status: {0}", response.getStatusLine());
            EntityUtils.consume(entity);
            LOG.log(Level.INFO, "*** Response entity: {0}", entity.toString());
        }
    }
}

public static RequestConfig configureRequest() {
    HttpHost proxy = new HttpHost("changeit.local", 8080, "http");
    RequestConfig config = RequestConfig.custom()
            .setProxy(proxy)
            .build();
    return config;
}

public static SSLContext createSslCustomContext() throws KeyStoreException, IOException, NoSuchAlgorithmException, CertificateException, KeyManagementException, UnrecoverableKeyException {
    // Trusted CA keystore
    KeyStore tks = KeyStore.getInstance(CA_KEYSTORE_TYPE);
    tks.load(new FileInputStream(CA_KEYSTORE_PATH), CA_KEYSTORE_PASS.toCharArray());

    // Client keystore
    KeyStore cks = KeyStore.getInstance(CLIENT_KEYSTORE_TYPE);
    cks.load(new FileInputStream(CLIENT_KEYSTORE_PATH), CLIENT_KEYSTORE_PASS.toCharArray());

    SSLContext sslcontext = SSLContexts.custom()
            //.loadTrustMaterial(tks, new TrustSelfSignedStrategy()) // use it to customize
            .loadKeyMaterial(cks, CLIENT_KEYSTORE_PASS.toCharArray()) // load client certificate
            .build();
    return sslcontext;
}

}

For those of you who simply want to set up a two-way authentication (server and client certificates), a combination of these two links will get you there :

Two-way auth setup:

https://linuxconfig.org/apache-web-server-ssl-authentication

You don't need to use the openssl config file that they mention; just use

• $ openssl genrsa -des3 -out ca.key 4096

• $ openssl req -new -x509 -days 365 -key ca.key -out ca.crt

to generate your own CA certificate, and then generate and sign the server and client keys via:

• $ openssl genrsa -des3 -out server.key 4096

• $ openssl req -new -key server.key -out server.csr

• $ openssl x509 -req -days 365 -in server.csr -CA ca.crt -CAkey ca.key -set_serial 100 -out server.crt

and

• $ openssl genrsa -des3 -out client.key 4096

• $ openssl req -new -key client.key -out client.csr

• $ openssl x509 -req -days 365 -in client.csr -CA ca.crt -CAkey ca.key -set_serial 101 -out client.crt

For the rest follow the steps in the link. Managing the certificates for Chrome works the same as in the example for firefox that is mentioned.

Next, setup the server via:

https://www.digitalocean.com/community/tutorials/how-to-create-a-ssl-certificate-on-apache-for-ubuntu-14-04

Note that you have already created the server .crt and .key so you don't have to do that step anymore.

Given a p12 file with both the certificate and the private key (generated by openssl, for example), the following code will use that for a specific HttpsURLConnection:

    KeyStore keyStore = KeyStore.getInstance("pkcs12");
    keyStore.load(new FileInputStream(keyStorePath), keystorePassword.toCharArray());
    KeyManagerFactory kmf = KeyManagerFactory.getInstance(KeyManagerFactory.getDefaultAlgorithm());
    kmf.init(keyStore, keystorePassword.toCharArray());
    SSLContext ctx = SSLContext.getInstance("TLS");
    ctx.init(kmf.getKeyManagers(), null, null);
    SSLSocketFactory sslSocketFactory = ctx.getSocketFactory();

    HttpsURLConnection connection = (HttpsURLConnection) url.openConnection();
    connection.setSSLSocketFactory(sslSocketFactory);

The SSLContext takes some time to initialize, so you might want to cache it.