ssh: add a factory for KeyPasswordProvider

Introduce a global default factory to create KeyPasswordProvider.
Previously, their creation was tied to the SSH session, but for SSH
signatures, we will need to be able to create KeyPasswordProviders
without having an SSH session.

Change-Id: If4a69c4d4c4e8de390cb1ef3b65966d0e39c24ff
Signed-off-by: Thomas Wolf <twolf@apache.org>

2 files changed, 86 insertions, 5 deletions

diff --git a/org.eclipse.jgit.ssh.apache/src/org/eclipse/jgit/transport/sshd/KeyPasswordProviderFactory.java b/org.eclipse.jgit.ssh.apache/src/org/eclipse/jgit/transport/sshd/KeyPasswordProviderFactory.java
new file mode 100644
index 0000000000..0537300b24
--- /dev/null
+++ b/org.eclipse.jgit.ssh.apache/src/org/eclipse/jgit/transport/sshd/KeyPasswordProviderFactory.java
@@ -0,0 +1,69 @@
+/*
+ * Copyright (C) 2024, Thomas Wolf <twolf@apache.org> and others
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Distribution License v. 1.0 which is available at
+ * https://www.eclipse.org/org/documents/edl-v10.php.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+package org.eclipse.jgit.transport.sshd;
+
+import java.util.concurrent.atomic.AtomicReference;
+import java.util.function.Function;
+
+import org.eclipse.jgit.annotations.NonNull;
+import org.eclipse.jgit.transport.CredentialsProvider;
+
+/**
+ * Maintains a static singleton instance of a factory to create a
+ * {@link KeyPasswordProvider} from a {@link CredentialsProvider}.
+ *
+ * @since 7.1
+ */
+public final class KeyPasswordProviderFactory {
+
+	/**
+	 * Creates a {@link KeyPasswordProvider} from a {@link CredentialsProvider}.
+	 */
+	@FunctionalInterface
+	public interface KeyPasswordProviderCreator
+			extends Function<CredentialsProvider, KeyPasswordProvider> {
+		// Nothing
+	}
+
+	private static final KeyPasswordProviderCreator DEFAULT = IdentityPasswordProvider::new;
+
+	private static AtomicReference<KeyPasswordProviderCreator> INSTANCE = new AtomicReference<>(
+			DEFAULT);
+
+	private KeyPasswordProviderFactory() {
+		// No instantiation
+	}
+
+	/**
+	 * Retrieves the currently set {@link KeyPasswordProviderCreator}.
+	 *
+	 * @return the {@link KeyPasswordProviderCreator}
+	 */
+	@NonNull
+	public static KeyPasswordProviderCreator getInstance() {
+		return INSTANCE.get();
+	}
+
+	/**
+	 * Sets a new {@link KeyPasswordProviderCreator}.
+	 *
+	 * @param provider
+	 *            to set; if {@code null}, sets a default provider.
+	 * @return the previously set {@link KeyPasswordProviderCreator}
+	 */
+	@NonNull
+	public static KeyPasswordProviderCreator setInstance(
+			KeyPasswordProviderCreator provider) {
+		if (provider == null) {
+			return INSTANCE.getAndSet(DEFAULT);
+		}
+		return INSTANCE.getAndSet(provider);
+	}
+}
diff --git a/org.eclipse.jgit.ssh.apache/src/org/eclipse/jgit/transport/sshd/SshdSessionFactory.java b/org.eclipse.jgit.ssh.apache/src/org/eclipse/jgit/transport/sshd/SshdSessionFactory.java
index 2c3cbe55c9..4a2eb9c3dd 100644
--- a/org.eclipse.jgit.ssh.apache/src/org/eclipse/jgit/transport/sshd/SshdSessionFactory.java
+++ b/org.eclipse.jgit.ssh.apache/src/org/eclipse/jgit/transport/sshd/SshdSessionFactory.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2018, 2022 Thomas Wolf <thomas.wolf@paranor.ch> and others
+ * Copyright (C) 2018, 2024 Thomas Wolf <twolf@apache.org> and others
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Distribution License v. 1.0 which is available at
@@ -210,7 +210,7 @@ public class SshdSessionFactory extends SshSessionFactory implements Closeable {
 						home, sshDir);
 				KeyIdentityProvider defaultKeysProvider = toKeyIdentityProvider(
 						getDefaultKeys(sshDir));
-				Supplier<KeyPasswordProvider> keyPasswordProvider = () -> createKeyPasswordProvider(
+				Supplier<KeyPasswordProvider> keyPasswordProvider = newKeyPasswordProvider(
 						credentialsProvider);
 				SshClient client = ClientBuilder.builder()
 						.factory(JGitSshClient::new)
@@ -574,12 +574,24 @@ public class SshdSessionFactory extends SshSessionFactory implements Closeable {
 	 * @param provider
 	 *            the {@link CredentialsProvider} to delegate to for user
 	 *            interactions
-	 * @return a new {@link KeyPasswordProvider}
+	 * @return a new {@link KeyPasswordProvider}, or {@code null} to use the
+	 *         global {@link KeyPasswordProviderFactory}
 	 */
-	@NonNull
 	protected KeyPasswordProvider createKeyPasswordProvider(
 			CredentialsProvider provider) {
-		return new IdentityPasswordProvider(provider);
+		return null;
+	}
+
+	private Supplier<KeyPasswordProvider> newKeyPasswordProvider(
+			CredentialsProvider credentials) {
+		return () -> {
+			KeyPasswordProvider provider = createKeyPasswordProvider(
+					credentials);
+			if (provider != null) {
+				return provider;
+			}
+			return KeyPasswordProviderFactory.getInstance().apply(credentials);
+		};
 	}
 
 	/**