Add ssh tests for PreferredAuthentications

Tests that it works with unknown authentications in the list, and
fails if there are no common authentications between server and
client. The latter also tests that the ssh config setting is taken
into account at all.

And promptly the JGit sshd client didn't. Add a fix for this. It's
a tiny bit hacky: Apache MINA looks up a custom property set on a
hierarchy of "PropertyResolver"s starting with the session. On the
session itself this property can never be set since it's read
already in the session constructor before anyone had any chance
to set it. The next element in the resolver hierarchy is the sshd
SshClient, and so we set that property there. Since we use one
SshClient and one ClientSession per JGit SshdSession, this is OK.

Bug: 520927
Change-Id: I62446fc1fffde125a8965c030240f0918ae234b7
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>

org.eclipse.jgit.ssh.apache/META-INF/MANIFEST.MF

@@ -51,6 +51,7 @@ Import-Package: org.apache.sshd.agent;version="[2.0.0,2.1.0)",
  org.apache.sshd.common.digest;version="[2.0.0,2.1.0)",
  org.apache.sshd.common.forward;version="[2.0.0,2.1.0)",
  org.apache.sshd.common.future;version="[2.0.0,2.1.0)",
+ org.apache.sshd.common.helpers;version="[2.0.0,2.1.0)",
  org.apache.sshd.common.io;version="[2.0.0,2.1.0)",
  org.apache.sshd.common.kex;version="[2.0.0,2.1.0)",
  org.apache.sshd.common.keyprovider;version="[2.0.0,2.1.0)",

org.eclipse.jgit.ssh.apache/src/org/eclipse/jgit/internal/transport/sshd/JGitSshClient.java

@@ -82,6 +82,12 @@ import org.eclipse.jgit.transport.sshd.KeyCache;
  */
 public class JGitSshClient extends SshClient {
 
+	/**
+	 * An attribute key for the comma-separated list of default preferred
+	 * authentication mechanisms.
+	 */
+	public static final AttributeKey<String> PREFERRED_AUTHENTICATIONS = new AttributeKey<>();
+
 	private KeyCache keyCache;
 
 	private CredentialsProvider credentialsProvider;
@@ -109,10 +115,24 @@ public class JGitSshClient extends SshClient {
 				userName + '@' + address, null);
 		SshFutureListener<IoConnectFuture> listener = createConnectCompletionListener(
 				connectFuture, userName, address, hostConfig);
+		// sshd needs some entries from the host config already in the
+		// constructor of the session. Put those as properties on this client,
+		// where it will find them. We can set the host config only once the
+		// session object has been created.
+		copyProperty(
+				hostConfig.getProperty(SshConstants.PREFERRED_AUTHENTICATIONS,
+						getAttribute(PREFERRED_AUTHENTICATIONS)),
+				PREFERRED_AUTHS);
 		connector.connect(address).addListener(listener);
 		return connectFuture;
 	}
 
+	private void copyProperty(String value, String key) {
+		if (value != null && !value.isEmpty()) {
+			getProperties().put(key, value);
+		}
+	}
+
 	private SshFutureListener<IoConnectFuture> createConnectCompletionListener(
 			ConnectFuture connectFuture, String username,
 			InetSocketAddress address, HostConfigEntry hostConfig) {

org.eclipse.jgit.ssh.apache/src/org/eclipse/jgit/transport/sshd/SshdSessionFactory.java

@@ -217,6 +217,12 @@ public class SshdSessionFactory extends SshSessionFactory implements Closeable {
 				JGitSshClient jgitClient = (JGitSshClient) client;
 				jgitClient.setKeyCache(getKeyCache());
 				jgitClient.setCredentialsProvider(credentialsProvider);
+				String defaultAuths = getDefaultPreferredAuthentications();
+				if (defaultAuths != null) {
+					jgitClient.setAttribute(
+							JGitSshClient.PREFERRED_AUTHENTICATIONS,
+							defaultAuths);
+				}
 				// Other things?
 				return client;
 			});
@@ -433,4 +439,17 @@ public class SshdSessionFactory extends SshSessionFactory implements Closeable {
 						UserAuthKeyboardInteractiveFactory.INSTANCE,
 						UserAuthPasswordFactory.INSTANCE));
 	}
+
+	/**
+	 * Gets the list of default preferred authentication mechanisms. If
+	 * {@code null} is returned the openssh default list will be in effect. If
+	 * the ssh config defines {@code PreferredAuthentications} the value from
+	 * the ssh config takes precedence.
+	 *
+	 * @return a comma-separated list of algorithm names, or {@code null} if
+	 *         none
+	 */
+	protected String getDefaultPreferredAuthentications() {
+		return null;
+	}
 }

org.eclipse.jgit.test/src/org/eclipse/jgit/transport/ssh/SshTestBase.java

@@ -572,6 +572,29 @@ public abstract class SshTestBase extends SshTestHarness {
 				"HostKeyAlgorithms ssh-rsa,ssh-dss");
 	}
 
+	@Test
+	public void testSshWithUnknownAuthInConfig() throws Exception {
+		cloneWith("ssh://git/doesntmatter", defaultCloneDir, null, //
+				"Host git", //
+				"HostName localhost", //
+				"Port " + testPort, //
+				"User " + TEST_USER, //
+				"IdentityFile " + privateKey1.getAbsolutePath(), //
+				"PreferredAuthentications gssapi-with-mic,hostbased,publickey,keyboard-interactive,password");
+	}
+
+	@Test(expected = TransportException.class)
+	public void testSshWithNoMatchingAuthInConfig() throws Exception {
+		// Server doesn't do password, and anyway we set no password.
+		cloneWith("ssh://git/doesntmatter", defaultCloneDir, null, //
+				"Host git", //
+				"HostName localhost", //
+				"Port " + testPort, //
+				"User " + TEST_USER, //
+				"IdentityFile " + privateKey1.getAbsolutePath(), //
+				"PreferredAuthentications password");
+	}
+
 	@Theory
 	public void testSshKeys(String keyName) throws Exception {
 		// JSch fails on ECDSA 384/521 keys. Compare