Add Session.purgeDirectoryCache()

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

@@ -311,6 +311,18 @@ public class Session {
         return resourceMap.get() != null;
     }
 
+    /**
+     * Purges the directory cache. Makes sure that a fresh copy of the directory will be
+     * read from the CA on the next time the directory is accessed.
+     *
+     * @since 3.0.0
+     */
+    public void purgeDirectoryCache() {
+        setDirectoryLastModified(null);
+        setDirectoryExpires(null);
+        resourceMap.set(null);
+    }
+
     /**
      * Reads the provider's directory, then rebuild the resource map. The resource map
      * is unchanged if the {@link AcmeProvider} returns that the directory has not been

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

@@ -97,6 +97,13 @@ public class SessionTest {
         assertThat(session.getDirectoryLastModified()).isEqualTo(now);
         session.setDirectoryLastModified(null);
         assertThat(session.getDirectoryLastModified()).isNull();
+
+        session.setDirectoryExpires(now);
+        session.setDirectoryLastModified(now);
+        session.purgeDirectoryCache();
+        assertThat(session.getDirectoryExpires()).isNull();
+        assertThat(session.getDirectoryLastModified()).isNull();
+        assertThat(session.hasDirectory()).isFalse();
     }
 
     /**