Also find challenges by class type

acme4j-client/src/main/java/org/shredzone/acme4j/Authorization.java

@@ -116,7 +116,6 @@ public class Authorization extends AcmeJsonResource {
      * @throws ClassCastException
      *             if the type does not match the expected Challenge class type
      */
-    @SuppressWarnings("unchecked")
     @CheckForNull
     public <T extends Challenge> T findChallenge(final String type) {
         return (T) getChallenges().stream()
@@ -125,6 +124,25 @@ public class Authorization extends AcmeJsonResource {
                 .orElse(null);
     }
 
+    /**
+     * Finds a {@link Challenge} of the given class type. Responding to this {@link
+     * Challenge} is sufficient for authorization.
+     *
+     * @param type
+     *         Challenge type (e.g. "Http01Challenge.class")
+     * @return {@link Challenge} of that type, or {@code null} if there is no such
+     * challenge, or if the challenge alone is not sufficient for authorization.
+     * @since 2.8
+     */
+    @CheckForNull
+    public <T extends Challenge> T findChallenge(Class<T> type) {
+        return getChallenges().stream()
+                .filter(type::isInstance)
+                .map(type::cast)
+                .reduce((a, b) -> {throw new AcmeProtocolException("Found more than one challenge of type " + type.getName());})
+                .orElse(null);
+    }
+
     /**
      * Permanently deactivates the {@link Authorization}.
      */

acme4j-client/src/test/java/org/shredzone/acme4j/AuthorizationTest.java

@@ -76,6 +76,30 @@ public class AuthorizationTest {
         assertThat(c4, is(instanceOf(TlsAlpn01Challenge.class)));
     }
 
+    /**
+     * Test that {@link Authorization#findChallenge(Class)} finds challenges.
+     */
+    @Test
+    public void testFindChallengeByType() throws IOException {
+        Authorization authorization = createChallengeAuthorization();
+
+        // A snail mail challenge is not available at all
+        NonExistingChallenge c1 = authorization.findChallenge(NonExistingChallenge.class);
+        assertThat(c1, is(nullValue()));
+
+        // HttpChallenge is available
+        Http01Challenge c2 = authorization.findChallenge(Http01Challenge.class);
+        assertThat(c2, is(notNullValue()));
+
+        // Dns01Challenge is available
+        Dns01Challenge c3 = authorization.findChallenge(Dns01Challenge.class);
+        assertThat(c3, is(notNullValue()));
+
+        // TlsAlpn01Challenge is available
+        TlsAlpn01Challenge c4 = authorization.findChallenge(TlsAlpn01Challenge.class);
+        assertThat(c4, is(notNullValue()));
+    }
+
     /**
      * Test that {@link Authorization#findChallenge(String)} fails on duplicate
      * challenges.
@@ -329,4 +353,13 @@ public class AuthorizationTest {
         }
     }
 
+    /**
+     * Dummy challenge that is never going to be created.
+     */
+    private static class NonExistingChallenge extends Challenge {
+        public NonExistingChallenge(Login login, JSON data) {
+            super(login, data);
+        }
+    }
+
 }

acme4j-example/src/main/java/org/shredzone/acme4j/ClientTest.java

@@ -304,7 +304,7 @@ public class ClientTest {
      */
     public Challenge httpChallenge(Authorization auth) throws AcmeException {
         // Find a single http-01 challenge
-        Http01Challenge challenge = auth.findChallenge(Http01Challenge.TYPE);
+        Http01Challenge challenge = auth.findChallenge(Http01Challenge.class);
         if (challenge == null) {
             throw new AcmeException("Found no " + Http01Challenge.TYPE + " challenge, don't know what to do...");
         }

src/site/markdown/usage/order.md

@@ -33,10 +33,11 @@ The `Authorization` instance contains further details about how you can prove ow
 
 `getChallenges()` returns a collection of all `Challenge`s offered by the CA for domain ownership validation. You only need to complete _one_ of them to successfully authorize your domain.
 
-The simplest way is to invoke `findChallenge()`, stating the challenge type your system is able to provide:
+The simplest way is to invoke `findChallenge()`, stating the challenge type your system is able to provide (either as challenge name or challenge class type):
 
 ```java
-Http01Challenge challenge = auth.findChallenge(Http01Challenge.TYPE);
+Http01Challenge challenge = auth.findChallenge(Http01Challenge.TYPE); // by name
+Http01Challenge challenge = auth.findChallenge(Http01Challenge.class); // by type
 ```
 
 It returns a properly casted `Challenge` object, or `null` if your challenge type was not acceptable. In this example, your system is able to respond to a [http-01](../challenge/http-01.html) challenge.