How can I test HMAC authentication using Dropwizar

I'm just getting started with Dropwizard 0.4.0, and I would like some help with HMAC authentication. Has anybody got any advice?

Thank you in advance.

At present Dropwizard doesn't support HMAC authentication right out of the box, so you'd have to write your own authenticator. A typical choice for HMAC authentication is to use the HTTP Authorization header. The following code expects this header in the following format:

Authorization: <algorithm> <apiKey> <digest>

An example would be

Authorization: HmacSHA1 abcd-efgh-1234 sdafkljlkansdaflk2354jlkj5345345dflkmsdf

The digest is built from the content of the body (marshalled entity) prior to URL encoding with the HMAC shared secret appended as base64. For a non-body request, such as GET or HEAD, the content is taken as the complete URI path and parameters with the secret key appended.

To implement this in a way that Dropwizard can work with it requires you to copy the BasicAuthenticator code present in the dropwizard-auth module into your own code and modify it with something like this:

import com.google.common.base.Optional;
import com.sun.jersey.api.core.HttpContext;
import com.sun.jersey.server.impl.inject.AbstractHttpContextInjectable;
import com.yammer.dropwizard.auth.AuthenticationException;
import com.yammer.dropwizard.auth.Authenticator;

import javax.ws.rs.WebApplicationException;
import javax.ws.rs.core.HttpHeaders;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.Response;

class HmacAuthInjectable<T> extends AbstractHttpContextInjectable<T> {
  private static final String PREFIX = "HmacSHA1";
  private static final String HEADER_VALUE = PREFIX + " realm=\"%s\"";

  private final Authenticator<HmacCredentials, T> authenticator;
  private final String realm;
  private final boolean required;

  HmacAuthInjectable(Authenticator<HmacCredentials, T> authenticator, String realm, boolean required) {
    this.authenticator = authenticator;
    this.realm = realm;
    this.required = required;
  }

  public Authenticator<HmacCredentials, T> getAuthenticator() {
    return authenticator;
  }

  public String getRealm() {
    return realm;
  }

  public boolean isRequired() {
    return required;
  }

  @Override
  public T getValue(HttpContext c) {

    try {
      final String header = c.getRequest().getHeaderValue(HttpHeaders.AUTHORIZATION);
      if (header != null) {

        final String[] authTokens = header.split(" ");

        if (authTokens.length != 3) {
          // Malformed
          HmacAuthProvider.LOG.debug("Error decoding credentials (length is {})", authTokens.length);
          throw new WebApplicationException(Response.Status.BAD_REQUEST);
        }

        final String algorithm = authTokens[0];
        final String apiKey = authTokens[1];
        final String signature = authTokens[2];
        final String contents;

        // Determine which part of the request will be used for the content
        final String method = c.getRequest().getMethod().toUpperCase();
        if ("GET".equals(method) ||
          "HEAD".equals(method) ||
          "DELETE".equals(method)) {
          // No entity so use the URI
          contents = c.getRequest().getRequestUri().toString();
        } else {
          // Potentially have an entity (even in OPTIONS) so use that
          contents = c.getRequest().getEntity(String.class);
        }

        final HmacCredentials credentials = new HmacCredentials(algorithm, apiKey, signature, contents);

        final Optional<T> result = authenticator.authenticate(credentials);
        if (result.isPresent()) {
          return result.get();
        }
      }
    } catch (IllegalArgumentException e) {
      HmacAuthProvider.LOG.debug(e, "Error decoding credentials");
    } catch (AuthenticationException e) {
      HmacAuthProvider.LOG.warn(e, "Error authenticating credentials");
      throw new WebApplicationException(Response.Status.INTERNAL_SERVER_ERROR);
    }

    if (required) {
      throw new WebApplicationException(Response.status(Response.Status.UNAUTHORIZED)
        .header(HttpHeaders.AUTHORIZATION,
          String.format(HEADER_VALUE, realm))
        .entity("Credentials are required to access this resource.")
        .type(MediaType.TEXT_PLAIN_TYPE)
        .build());
    }
    return null;
  }
}

The above is not perfect, but it'll get you started. You may want to refer to the MultiBit Merchant release candidate source code (MIT license) for a more up to date version and the various supporting classes.

The next step is to integrate the authentication process into your ResourceTest subclass. Unfortunately, Dropwizard doesn't provide a good entry point for authentication providers in v0.4.0, so you may want to introduce your own base class, similar to this:

import com.google.common.collect.Lists;
import com.google.common.collect.Sets;
import com.sun.jersey.api.client.Client;
import com.sun.jersey.test.framework.AppDescriptor;
import com.sun.jersey.test.framework.JerseyTest;
import com.sun.jersey.test.framework.LowLevelAppDescriptor;
import com.xeiam.xchange.utils.CryptoUtils;
import com.yammer.dropwizard.bundles.JavaBundle;
import com.yammer.dropwizard.jersey.DropwizardResourceConfig;
import com.yammer.dropwizard.jersey.JacksonMessageBodyProvider;
import com.yammer.dropwizard.json.Json;
import org.codehaus.jackson.map.Module;
import org.junit.After;
import org.junit.Before;
import org.multibit.mbm.auth.hmac.HmacAuthProvider;
import org.multibit.mbm.auth.hmac.HmacAuthenticator;
import org.multibit.mbm.persistence.dao.UserDao;
import org.multibit.mbm.persistence.dto.User;
import org.multibit.mbm.persistence.dto.UserBuilder;

import java.io.UnsupportedEncodingException;
import java.security.GeneralSecurityException;
import java.util.List;
import java.util.Set;

import static org.mockito.Mockito.mock;
import static org.mockito.Mockito.when;

/**
* A base test class for testing Dropwizard resources.
*/
public abstract class BaseResourceTest {
  private final Set<Object> singletons = Sets.newHashSet();
  private final Set<Object> providers = Sets.newHashSet();
  private final List<Module> modules = Lists.newArrayList();

  private JerseyTest test;

  protected abstract void setUpResources() throws Exception;

  protected void addResource(Object resource) {
    singletons.add(resource);
  }

  public void addProvider(Object provider) {
    providers.add(provider);
  }

  protected void addJacksonModule(Module module) {
    modules.add(module);
  }

  protected Json getJson() {
    return new Json();
  }

  protected Client client() {
    return test.client();
  }

  @Before
  public void setUpJersey() throws Exception {
    setUpResources();
    this.test = new JerseyTest() {
      @Override
      protected AppDescriptor configure() {
        final DropwizardResourceConfig config = new DropwizardResourceConfig();
        for (Object provider : JavaBundle.DEFAULT_PROVIDERS) { // sorry, Scala folks
          config.getSingletons().add(provider);
        }
        for (Object provider : providers) {
          config.getSingletons().add(provider);
        }
        Json json = getJson();
        for (Module module : modules) {
          json.registerModule(module);
        }
        config.getSingletons().add(new JacksonMessageBodyProvider(json));
        config.getSingletons().addAll(singletons);
        return new LowLevelAppDescriptor.Builder(config).build();
      }
    };
    test.setUp();
  }

  @After
  public void tearDownJersey() throws Exception {
    if (test != null) {
      test.tearDown();
    }
  }

  /**
* @param contents The content to sign with the default HMAC process (POST body, GET resource path)
* @return
*/
  protected String buildHmacAuthorization(String contents, String apiKey, String secretKey) throws UnsupportedEncodingException, GeneralSecurityException {
    return String.format("HmacSHA1 %s %s",apiKey, CryptoUtils.computeSignature("HmacSHA1", contents, secretKey));
  }

  protected void setUpAuthenticator() {
    User user = UserBuilder
      .getInstance()
      .setUUID("abc123")
      .setSecretKey("def456")
      .build();

    //
    UserDao userDao = mock(UserDao.class);
    when(userDao.getUserByUUID("abc123")).thenReturn(user);

    HmacAuthenticator authenticator = new HmacAuthenticator();
    authenticator.setUserDao(userDao);

    addProvider(new HmacAuthProvider<User>(authenticator, "REST"));
  }
}

Again, the above code is not perfect, but the idea is to allow a mocked up UserDao to provide a standard user with a known shared secret key. You'd have to introduce your own UserBuilder implementation for testing purposes.

Finally, with the above code a Dropwizard Resource that had an endpoint like this:

import com.google.common.base.Optional;
import com.yammer.dropwizard.auth.Auth;
import com.yammer.metrics.annotation.Timed;
import org.multibit.mbm.core.Saying;
import org.multibit.mbm.persistence.dto.User;

import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import javax.ws.rs.QueryParam;
import javax.ws.rs.core.MediaType;
import java.util.concurrent.atomic.AtomicLong;

@Path("/")
@Produces(MediaType.APPLICATION_JSON)
public class HelloWorldResource {
  private final String template;
  private final String defaultName;
  private final AtomicLong counter;

  public HelloWorldResource(String template, String defaultName) {
    this.template = template;
    this.defaultName = defaultName;
    this.counter = new AtomicLong();
  }

  @GET
  @Timed
  @Path("/hello-world")
  public Saying sayHello(@QueryParam("name") Optional<String> name) {
    return new Saying(counter.incrementAndGet(),
      String.format(template, name.or(defaultName)));
  }

  @GET
  @Timed
  @Path("/secret")
  public Saying saySecuredHello(@Auth User user) {
    return new Saying(counter.incrementAndGet(),
      "You cracked the code!");
  }

}

could be tested with a unit test that was configured like this:

import org.junit.Test;
import org.multibit.mbm.core.Saying;
import org.multibit.mbm.test.BaseResourceTest;

import javax.ws.rs.core.HttpHeaders;

import static org.junit.Assert.assertEquals;

public class HelloWorldResourceTest extends BaseResourceTest {


  @Override
  protected void setUpResources() {
    addResource(new HelloWorldResource("Hello, %s!","Stranger"));

    setUpAuthenticator();
  }

  @Test
  public void simpleResourceTest() throws Exception {

    Saying expectedSaying = new Saying(1,"Hello, Stranger!");

    Saying actualSaying = client()
      .resource("/hello-world")
      .get(Saying.class);

    assertEquals("GET hello-world returns a default",expectedSaying.getContent(),actualSaying.getContent());

  }


  @Test
  public void hmacResourceTest() throws Exception {

    String authorization = buildHmacAuthorization("/secret", "abc123", "def456");

    Saying actual = client()
      .resource("/secret")
      .header(HttpHeaders.AUTHORIZATION, authorization)
      .get(Saying.class);

    assertEquals("GET secret returns unauthorized","You cracked the code!", actual.getContent());

  }


}

Hope this helps you get started.