Add ConsolePasswordFinder to read from Console

* There was no example `PasswordFinder` to prompt
a user for their password

src/main/java/net/schmizz/sshj/userauth/password/ConsolePasswordFinder.java

@@ -0,0 +1,52 @@
+/*
+ * Copyright (C)2009 - SSHJ Contributors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package net.schmizz.sshj.userauth.password;
+
+import java.io.Console;
+
+/** A PasswordFinder that reads a password from a console */
+public class ConsolePasswordFinder implements PasswordFinder {
+
+    private final Console console;
+
+    /**
+     * Initializes with the System Console, which will be null if not run from an interactive shell.
+     */
+    public ConsolePasswordFinder() {
+        this(System.console());
+    }
+
+    /**
+     * @param console the console to read the password from.  May be null.
+     */
+    public ConsolePasswordFinder(Console console) {
+        this.console = console;
+    }
+
+    @Override
+    public char[] reqPassword(Resource<?> resource) {
+        if (console == null) {
+            // the request cannot be serviced
+            return null;
+        }
+        return console.readPassword("Enter passphrase for %s:", resource.toString());
+    }
+
+    @Override
+    public boolean shouldRetry(Resource<?> resource) {
+        return true;
+    }
+}

src/test/java/net/schmizz/sshj/userauth/password/TestConsolePasswordFinder.java

@@ -0,0 +1,36 @@
+/*
+ * Copyright (C)2009 - SSHJ Contributors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package net.schmizz.sshj.userauth.password;
+
+import org.junit.Assert;
+import org.junit.Test;
+import org.mockito.Mockito;
+
+public class TestConsolePasswordFinder {
+
+    /*
+     * Note that Mockito 1.9 cannot mock Console because it is a final class,
+     * so there are no other tests.
+     */
+
+    @Test
+    public void testReqPasswordNullConsole() {
+        char[] password = new ConsolePasswordFinder(null)
+            .reqPassword(Mockito.mock(Resource.class));
+        Assert.assertNull("Password should be null with null console", password);
+    }
+
+}