Revert "SSH: Simplify CachingPublicKeyAuthenticator implementation"

This change is not compatible with SSHD 0.9.0 which is being brought
into master by merges from stable-2.9

This reverts commit 64d12ce359.

Change-Id: Ib0ae8603c5d6d04f8df76775566418f12a0fc7c1

gerrit-sshd/src/main/java/com/google/gerrit/sshd/CachingPublicKeyAuthenticator.java

@@ -17,12 +17,56 @@ package com.google.gerrit.sshd;
 import com.google.inject.Inject;
 import com.google.inject.Singleton;
 
+import org.apache.sshd.common.Session;
+import org.apache.sshd.common.SessionListener;
+import org.apache.sshd.server.PublickeyAuthenticator;
+import org.apache.sshd.server.session.ServerSession;
+
+import java.security.PublicKey;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+
 @Singleton
-public class CachingPublicKeyAuthenticator
+public class CachingPublicKeyAuthenticator implements PublickeyAuthenticator,
-    extends org.apache.sshd.server.auth.CachingPublicKeyAuthenticator {
+    SessionListener {
+
+  private final PublickeyAuthenticator authenticator;
+  private final Map<ServerSession, Map<PublicKey, Boolean>> sessionCache;
 
   @Inject
   public CachingPublicKeyAuthenticator(DatabasePubKeyAuth authenticator) {
-    super(authenticator);
+    this.authenticator = authenticator;
+    this.sessionCache = new ConcurrentHashMap<>();
+  }
+
+  @Override
+  public boolean authenticate(String username, PublicKey key,
+      ServerSession session) {
+    Map<PublicKey, Boolean> m = sessionCache.get(session);
+    if (m == null) {
+      m = new HashMap<>();
+      sessionCache.put(session, m);
+      session.addListener(this);
+    }
+    if (m.containsKey(key)) {
+      return m.get(key);
+    }
+    boolean r = authenticator.authenticate(username, key, session);
+    m.put(key, r);
+    return r;
+  }
+
+  @Override
+  public void sessionCreated(Session session) {
+  }
+
+  @Override
+  public void sessionEvent(Session sesssion, Event event) {
+  }
+
+  @Override
+  public void sessionClosed(Session session) {
+    sessionCache.remove(session);
   }
 }