Enables client authentification for SSL

Client authentification can be set as with the SSL Properties to
require the client certificate to be signed by the server.
Added jUnit test and test certificates

broker/src/main/java/io/moquette/server/DefaultMoquetteSslContextCreator.java

@@ -23,6 +23,9 @@ import org.slf4j.LoggerFactory;
 
 import javax.net.ssl.KeyManagerFactory;
 import javax.net.ssl.SSLContext;
+import javax.net.ssl.TrustManager;
+import javax.net.ssl.TrustManagerFactory;
+
 import java.io.*;
 import java.net.URL;
 import java.security.*;
@@ -69,6 +72,11 @@ class DefaultMoquetteSslContextCreator implements ISslContextCreator {
             return null;
         }
 
+		// if client authentification is enabled a trustmanager needs to be
+		// added to the ServerContext
+		String sNeedsClientAuth = props.getProperty(BrokerConstants.NEED_CLIENT_AUTH, "false");
+		boolean needsClientAuth = Boolean.valueOf(sNeedsClientAuth);
+
         try {
             InputStream jksInputStream = jksDatastore(jksPath);
             SSLContext serverContext = SSLContext.getInstance("TLS");
@@ -76,7 +84,16 @@ class DefaultMoquetteSslContextCreator implements ISslContextCreator {
             ks.load(jksInputStream, keyStorePassword.toCharArray());
             final KeyManagerFactory kmf = KeyManagerFactory.getInstance(KeyManagerFactory.getDefaultAlgorithm());
             kmf.init(ks, keyManagerPassword.toCharArray());
-            serverContext.init(kmf.getKeyManagers(), null, null);
+			TrustManager[] trustManagers = null;
+			if (needsClientAuth) {
+				// use keystore as truststore, as server needs to trust certificates signed by the server certificates
+				TrustManagerFactory tmf = TrustManagerFactory.getInstance(TrustManagerFactory.getDefaultAlgorithm());
+				tmf.init(ks);
+				trustManagers = tmf.getTrustManagers();
+			}
+			// init sslContext
+			serverContext.init(kmf.getKeyManagers(), trustManagers, null);
+
             return serverContext;
         } catch (NoSuchAlgorithmException | UnrecoverableKeyException | CertificateException | KeyStoreException
                 | KeyManagementException | IOException ex) {