Remove to-be-deprecated OOB OAuth flow in nomulus login (#1625)

core/src/main/java/google/registry/tools/ForwardingServerReceiver.java

@@ -0,0 +1,72 @@
+// Copyright 2022 The Nomulus Authors. All Rights Reserved.
+//
+// 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 google.registry.tools;
+
+import com.google.api.client.extensions.java6.auth.oauth2.VerificationCodeReceiver;
+import com.google.api.client.extensions.jetty.auth.oauth2.LocalServerReceiver;
+import java.io.IOException;
+
+/**
+ * A thin wrapper around {@link LocalServerReceiver} which points the redirect URI to a different
+ * port (the forwarding port) while still listening on the random unused port (the remote port)
+ * nomulus itself picks. This allows us to run the nomulus tool on a remote host (which one can SSH
+ * into) while performing the OAuth 3-legged login flow in a local browser (from the lost host where
+ * the SSH client resides).
+ *
+ * <p>When performing the login flow, an HTTP server will be listening on the remote port and have a
+ * redirect_uri of <code>http://localhost:remote_port</code>, which is only accessible from the
+ * remote host. By changing the redirect_uri to <code>http://localhost:forwarding_port</code>, it
+ * becomes accessible from the local host, if <code>local_host:forwarding_port</code> is forwarded
+ * to <code>remote_host:remote_port</code>.
+ *
+ * <p>Note that port forwarding is <b>required</b>. We cannot use the remote host's IP or reverse
+ * DNS address in the redirect URI, even if they are directly accessible from the local host,
+ * because the only allowed redirect URI scheme for desktops apps when sending a request to the
+ * Google OAuth server is the loopback address with a port.
+ *
+ * @see <href
+ *     a=https://developers.google.com/identity/protocols/oauth2/native-app#request-parameter-redirect_uri>
+ *     redirect_uri values </href>
+ */
+final class ForwardingServerReceiver implements VerificationCodeReceiver {
+
+  private final int forwarding_port;
+  private final LocalServerReceiver localServerReceiver = new LocalServerReceiver();
+
+  ForwardingServerReceiver(int forwarding_port) {
+    this.forwarding_port = forwarding_port;
+  }
+
+  @Override
+  public String getRedirectUri() throws IOException {
+    String redirect_uri = localServerReceiver.getRedirectUri();
+    return redirect_uri.replace("localhost:" + getRemotePort(), "localhost:" + forwarding_port);
+  }
+
+  @Override
+  public String waitForCode() throws IOException {
+    return localServerReceiver.waitForCode();
+  }
+
+  @Override
+  public void stop() throws IOException {
+    localServerReceiver.stop();
+    System.out.println("You can now exit from the SSH session created for port forwarding.");
+  }
+
+  int getRemotePort() {
+    return localServerReceiver.getPort();
+  }
+}

core/src/main/java/google/registry/tools/LoginCommand.java

@@ -19,7 +19,7 @@ import com.beust.jcommander.Parameters;
 import com.google.api.client.extensions.java6.auth.oauth2.AuthorizationCodeInstalledApp;
 import com.google.api.client.extensions.jetty.auth.oauth2.LocalServerReceiver;
 import com.google.api.client.googleapis.auth.oauth2.GoogleAuthorizationCodeFlow;
-import com.google.api.client.googleapis.extensions.java6.auth.oauth2.GooglePromptReceiver;
+import java.net.InetAddress;
 import javax.inject.Inject;
 
 /** Authorizes the nomulus tool for OAuth 2.0 access to remote resources. */
@@ -30,24 +30,35 @@ final class LoginCommand implements Command {
   @Inject @AuthModule.ClientScopeQualifier String clientScopeQualifier;
 
   @Parameter(
-      names = "--remote",
+      names = "--port",
       description =
-          "Whether the command is run on a remote host where access to a browser is not available. "
-              + "If set to true, a URL will be given and a code is expected to be entered after "
-              + "the user completes authorization by visiting that URL.")
-  private boolean remote = false;
+          "A free port on the local host. When set, it is assumed that the nomulus tool runs on a"
+              + " remote host whose browser is not accessible locally. i. e. if you SSH to a"
+              + " machine and run `nomulus` there, the ssh client is on the local host and nomulus"
+              + " runs on a remote host. You will need to forward the local port specified here to"
+              + " a remote port that nomulus randomly picks. Follow the instruction when prompted.")
+  private int port = 0;
 
   @Override
   public void run() throws Exception {
     AuthorizationCodeInstalledApp app;
-    if (remote) {
+    if (port != 0) {
+      String remote_host = InetAddress.getLocalHost().getHostName();
+      ForwardingServerReceiver forwardingServerReceiver = new ForwardingServerReceiver(port);
       app =
           new AuthorizationCodeInstalledApp(
               flow,
-              new GooglePromptReceiver(),
+              forwardingServerReceiver,
               url -> {
-                System.out.println("Please open the following address in your browser:");
-                System.out.println("  " + url);
+                int remote_port = forwardingServerReceiver.getRemotePort();
+                System.out.printf(
+                    "Please first run the following command in a separate terminal on your local "
+                        + "host:\n\n  ssh -L %s:localhost:%s %s\n\n",
+                    port, remote_port, remote_host);
+                System.out.printf(
+                    "Please then open the following URL in your local browser and follow the"
+                        + " instructions:\n\n  %s\n\n",
+                    url);
               });
     } else {
       app = new AuthorizationCodeInstalledApp(flow, new LocalServerReceiver());