When working with JSch (Java Secure Channel) for SSH connections, handling interactive prompts and keyboard-interactive authentication requires implementing the UserInfo and UIKeyboardInteractive interfaces provided by JSch. These interfaces allow you to interact with the user to gather necessary input for authentication (like passwords, passphrases, or other interactive challenges like 2FA).

Here’s a step-by-step process:

Steps to Handle Interactive Prompts

1. Implement the UserInfo Interface:
   This interface is used to provide and verify user credentials. For example, request a password or passphrase during authentication.
2. Implement the UIKeyboardInteractive Interface:
   This interface is used for keyboard-interactive authentication. This mechanism often includes dynamic prompts (e.g., security questions, OTP codes, etc.).
3. Attach the Implementation to the Session Object:
   Set your UserInfo implementation to the session using session.setUserInfo().
4. Connect to the Session:
   Once everything is set up, open the session and proceed with connecting to the host.

Code Example

Here’s an example of how to handle both interactive prompts and keyboard-interactive authentication using JSch:

package org.kodejava.jsch;

import com.jcraft.jsch.*;

public class JschKeyboardInteractiveExample {
   public static void main(String[] args) {
      String username = "username";
      String host = "example.com";
      int port = 22;

      JSch jsch = new JSch();
      try {
         Session session = jsch.getSession(username, host, port);

         // Set a UserInfo implementation
         session.setUserInfo(new MyUserInfo());

         // Connect to the session
         session.connect();

         System.out.println("Connected to the host successfully!");

         // Do your operations (e.g., execute commands) here...

         session.disconnect();
         System.out.println("Disconnected from the host.");
      } catch (Exception e) {
         e.printStackTrace();
      }
   }

   // Custom UserInfo implementation for interactive prompts
   public static class MyUserInfo implements UserInfo, UIKeyboardInteractive {
      private String password;

      // Constructor to provide password (or use a Scanner to collect input)
      public MyUserInfo() {
         // Replace this with actual input collection if required
         this.password = "password"; // Set your password here
      }

      @Override
      public String getPassword() {
         return password;
      }

      @Override
      public boolean promptYesNo(String message) {
         System.out.println("Prompt Yes/No: " + message);
         // Assuming 'Yes' for simplicity; implement actual logic if needed
         return true;
      }

      @Override
      public String getPassphrase() {
         return null; // Not using a passphrase for this example
      }

      @Override
      public boolean promptPassphrase(String message) {
         System.out.println("Prompt Passphrase: " + message);
         return false; // No passphrase in this example
      }

      @Override
      public boolean promptPassword(String message) {
         System.out.println("Prompt Password: " + message);
         return true; // Assuming the password is already set
      }

      @Override
      public void showMessage(String message) {
         System.out.println("Message: " + message);
      }

      @Override
      public String[] promptKeyboardInteractive(String destination, String name, String instruction, String[] prompt, boolean[] echo) {
         System.out.println("Keyboard Interactive Authentication:");
         System.out.println("Destination: " + destination);
         System.out.println("Name: " + name);
         System.out.println("Instruction: " + instruction);

         String[] responses = new String[prompt.length];
         for (int i = 0; i < prompt.length; i++) {
            System.out.println("Prompt: " + prompt[i]);
            // Collect input from the user (hardcoded for this example)
            responses[i] = this.password; // Assuming password for simplicity
         }
         return responses;
      }
   }
}

Explanation of Key Parts in the Code

1. UserInfo Methods:
   • getPassword(): Returns the password string (hard-coded or dynamically retrieved).
   • promptYesNo(String): Handles Yes/No prompts (like accepting host key verification).
   • getPassphrase() and promptPassphrase(String): Used if dealing with private key authentication and a passphrase is necessary.
   • showMessage(String): Displays generic messages from the server or library to the user.
2. UIKeyboardInteractive Methods:
   • promptKeyboardInteractive(...): Handles keyboard-interactive authentication challenges.
     Prompts can include questions for passwords, 2FA, CAPTCHA, etc.
3. Session Configuration:
   The setUserInfo() method attaches your custom implementation to the session, enabling interactive behavior during the connection process.

Output Examples

• If the server uses simple password authentication:

Connected to the host successfully!
Disconnected from the host.

• If the server uses keyboard-interactive challenges:

Keyboard Interactive Authentication:
Destination: example.com
Name: SSH Server
Instruction: Please respond to the following prompts:
Prompt: Password

Notes and Best Practices

1. Password Storage Security:
   Avoid hardcoding sensitive credentials in the code. Use environment variables, encrypted vaults, or secure input methods.
2. Dynamic Input Collection:
   Replace hardcoded strings with dynamic input collection (e.g., Scanner or a GUI dialog).
3. Error Handling:
   Handle exceptions for cases like invalid credentials, session interruptions, and server-side configuration issues.
4. Host Key Checking:
   JSch may require host key checking. Either configure the known hosts file or handle it manually in the promptYesNo method.

This approach allows you to securely and efficiently handle interactive prompts and keyboard authentication while using JSch in Java.

Maven Dependencies

<dependency>
    <groupId>com.jcraft</groupId>
    <artifactId>jsch</artifactId>
    <version>0.1.55</version>
</dependency>