SSL / TLS REST Server – Client with Spring and TomEE
When building a system, developers usually disregard the security aspects. Security has been always something very important to worry about, but it’s attracting even higher concerns than before. Just this year we had a few cases like the Heartbleed Bug or the CelebrityGate scandal. This has nothing to do with the post, but are just examples that security really matters and we should be aware of it.
With the increasing popularity of REST services it makes sense that these need to be secured in some way. A couple of weeks ago, I had to integrate my client with a REST service behind https. I have never done it before and that’s the reason for this post. I have to confess that I’m no security expert myself, so please correct me if I write anything stupid.
The Setup
For this example I have used the following setup:
I’m not going into many details about SSL and TSL, so please check here for additional content. Note that TLS is the new name for SSL evolution. Sometimes there is confusion between the two and people often say SSL, but use the newest version of TSL. Keep that in mind.
Don’t forget to follow the instructions on the following page to setup SSL for Tomcat: SSL Configuration HOW-TO. This is needed for the server to present the client with a set of credentials, a Certificate, to secure the connection between server and client.
The Code
Service
Let’s create a simple Spring REST Service:
RestService.java
1 2 3 4 5 6 7 8 9 | @Controller @RequestMapping("/") public class RestService { @RequestMapping(method = RequestMethod.GET) @ResponseBody public String get() { return "Called the get Rest Service"; } } |
And we also need some wiring for this to work:
RestConfig.java
1 2 3 4 | @Configuration @EnableWebMvc @ComponentScan(basePackages = "com.radcortez.rest.ssl") public class RestConfig {} |
web.xml
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 | <?xml version="1.0" encoding="UTF-8"?> <web-app version="3.1" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"> <servlet> <servlet-name>rest</servlet-name> <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class> <init-param> <param-name>contextClass</param-name> <param-value>org.springframework.web.context.support.AnnotationConfigWebApplicationContext</param-value> </init-param> <init-param> <param-name>contextConfigLocation</param-name> <param-value>com.radcortez.rest.ssl</param-value> </init-param> <load-on-startup>1</load-on-startup> </servlet> <servlet-mapping> <servlet-name>rest</servlet-name> <url-pattern>/</url-pattern> </servlet-mapping> <security-constraint> <web-resource-collection> <web-resource-name>Rest Application</web-resource-name> <url-pattern>/*</url-pattern> </web-resource-collection> <user-data-constraint> <!-- Needed for our application to respond to https requests --> <transport-guarantee>CONFIDENTIAL</transport-guarantee> </user-data-constraint> </security-constraint> </web-app> |
Please, note the elements security-constraint, user-data-constraint and <transport-guarantee>CONFIDENTIAL</transport-guarantee>. These are needed to specify that the application requires a secure connection. Check Securing Web Applications for Java Applications.
Running the Service
Just deploy the application on the TomEE Server using your favourite IDE environment and access https://localhost:8443/. You should get the following (you might need to accept the server certificate first):
Note that the browser protocol is https and the port is 8443 (assuming that you kept the default settings in SSL Configuration HOW-TO.
Client
Now, if you try to call this REST service with a Java client, most likely you are going to get the following message and Exception (or similar):
Message: I/O error on GET request for “https://localhost:8443/”:sun.security.validator.ValidatorException:
Exception: Caused by: javax.net.ssl.SSLHandshakeException: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
This happens because the running JDK does not have a valid certificate for your server. You can import it, and get rid of the problem, but let’s do something more interesting. We are going to programatically supply a trusted keystore with our server certificate.
This is especially useful if:
- you are running your code into multiple environments
- you don’t have to manually import the certificate into the JDK every time
- if you upgrade the JDK you have to remember about the certificates
- for some odd reason you don’t have access to the JDK itself to import the certificate
Let’s write some code:
RestClientConfig.java
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 | @Configuration @PropertySource("classpath:config.properties") public class RestClientConfig { @Bean public RestOperations restOperations(ClientHttpRequestFactory clientHttpRequestFactory) throws Exception { return new RestTemplate(clientHttpRequestFactory); } @Bean public ClientHttpRequestFactory clientHttpRequestFactory(HttpClient httpClient) { return new HttpComponentsClientHttpRequestFactory(httpClient); } @Bean public HttpClient httpClient(@Value("${keystore.file}") String file, @Value("${keystore.pass}") String password) throws Exception { KeyStore trustStore = KeyStore.getInstance(KeyStore.getDefaultType()); FileInputStream instream = new FileInputStream(new File(file)); try { trustStore.load(instream, password.toCharArray()); } finally { instream.close(); } SSLContext sslcontext = SSLContexts.custom().loadTrustMaterial(trustStore, new TrustSelfSignedStrategy()).build(); SSLConnectionSocketFactory sslsf = new SSLConnectionSocketFactory(sslcontext, new String[]{"TLSv1.2"}, null, BROWSER_COMPATIBLE_HOSTNAME_VERIFIER); return HttpClients.custom().setSSLSocketFactory(sslsf).build(); } @Bean public static PropertySourcesPlaceholderConfigurer propertySourcesPlaceholderConfigurer() { return new PropertySourcesPlaceholderConfigurer(); } } |
Here we use Spring RestOperations interface which specified a basic set of RESTful operations. Next we use Apache HTTP Components SSLConnectionSocketFactory which gives us the ability to validate the identity of the server against a list of trusted certificates. The certificate is loaded from the same file used on the server by KeyStore.
RestServiceClientIT.java
1 2 3 4 5 6 7 8 9 10 11 12 13 | @RunWith(SpringJUnit4ClassRunner.class) @ContextConfiguration(classes = RestClientConfig.class) public class RestServiceClientIT { @Autowired private RestOperations rest; @Test public void testRestRequest() throws Exception { ResponseEntity<String> response = rest.getForEntity("https://localhost:8443/", String.class); System.out.println("response = " + response); System.out.println("response.getBody() = " + response.getBody()); } } |
A simple test class. We also need a properties file with the keystore file location and password:
config.properties
1 2 | keystore.file=${user.home}/.keystore keystore.pass=changeit |
This should work fine if you used all the defaults.
Running the Test
If you now run the test which invokes the REST service within a Java client, you should get the following output:
Response: <200 OK,Called the get Rest Service,{Server=[Apache-Coyote/1.1], Cache-Control=[private], Expires=[Thu, 01 Jan 1970 01:00:00 WET], Content-Type=[text/plain;charset=ISO-8859-1], Content-Length=[27], Date=[Tue, 23 Dec 2014 01:29:20 GMT]}>
Body: Called the get Rest Service
Conclusion
That’s it! You can now call your REST service with your client in a secured manner. If you prefer to add the certificate to the JDK keystore, please check this post.
Stay tuned for an equivalent for Java EE JAX-RS equivalent.
Resources
You can clone a full working copy from my github repository: REST SSL.