Custom Callback Usage and Extension Techniques in ForgeRock AM

ForgeRock Access Management (AM) is a powerful platform for managing identity and access across various applications and services. One of its most flexible features is the ability to define and use custom callbacks, which allow developers to extend the platform’s functionality to meet specific business needs. In this article, we will explore how to implement and extend custom callbacks in ForgeRock AM, providing detailed examples and best practices.

Understanding Callbacks in ForgeRock AM

A callback in ForgeRock AM is a mechanism that allows the platform to interact with external systems or custom logic during the authentication or authorization process. Callbacks are typically used to collect additional information from the user, validate credentials, or integrate with third-party services.

ForgeRock AM provides a set of built-in callbacks, such as BasicAuthCallback for HTTP Basic Authentication and OAuth2Callback for OAuth 2.0. However, in many cases, organizations need to implement custom callbacks to handle unique scenarios. For example, you might need a custom callback to integrate with a legacy system, enforce custom security policies, or collect additional user attributes during authentication.

The Callback Execution Flow

To understand how custom callbacks work, it’s essential to grasp the execution flow of callbacks in ForgeRock AM. The typical flow is as follows:

1. Authentication Request: A user initiates an authentication request to access a protected resource.
2. Callback Selection: ForgeRock AM selects the appropriate callback(s) based on the configured authentication chain.
3. Callback Execution: The selected callback is executed, which may involve collecting user input, validating credentials, or interacting with external systems.
4. Result Processing: The result of the callback execution is processed, and the authentication flow continues or terminates based on the outcome.

This flow is highly customizable, allowing developers to inject custom logic at various points in the authentication process.

Implementing Custom Callbacks

To implement a custom callback in ForgeRock AM, you need to create a class that implements the org.forgerock.openam.auth.callback.CustomCallback interface. This interface provides methods for handling the callback execution and processing the results.

Example: Implementing a Custom Callback

Let’s walk through an example of implementing a custom callback that collects additional user attributes during authentication.

import org.forgerock.openam.auth.callback.CustomCallback;
import org.forgerock.openam.auth.callback.CustomCallbackContext;
import org.forgerock.openam.auth.callback.CustomCallbackResult;
import org.forgerock.openam.auth.callback.CustomCallbackType;
import org.forgerock.openam.auth.callback.CustomCallbackException;

public class CustomUserAttributeCallback implements CustomCallback {

    private String attributeName;

    public CustomUserAttributeCallback(String attributeName) {
        this.attributeName = attributeName;
    }

    @Override
    public void init(CustomCallbackContext context) throws CustomCallbackException {
        // Initialize the callback context
        context.setCallbackType(CustomCallbackType.USER_INPUT);
        context.setCallbackHelpText("Please provide the value for " + attributeName);
    }

    @Override
    public CustomCallbackResult process(CustomCallbackContext context) throws CustomCallbackException {
        // Process the user input
        String userInput = context.getUserInput();
        if (userInput == null || userInput.isEmpty()) {
            throw new CustomCallbackException("The attribute " + attributeName + " cannot be empty.");
        }

        // Create the result
        CustomCallbackResult result = new CustomCallbackResult();
        result.setSuccess(true);
        result.setResultData(userInput);

        return result;
    }

    @Override
    public void cleanup(CustomCallbackContext context) throws CustomCallbackException {
        // Cleanup resources if necessary
    }
}

Explanation

• Initialization (init method): This method is called when the callback is initialized. It sets the type of callback (in this case, USER_INPUT) and provides a help text to guide the user.
• Processing (process method): This method handles the user input. It checks if the input is valid and creates a result object that indicates whether the callback was successful.
• Cleanup (cleanup method): This method is used to release any resources that were allocated during the callback execution.

Registering the Custom Callback

Once you’ve implemented the custom callback, you need to register it with ForgeRock AM. This is typically done by adding the callback class to the classpath and configuring it in the AM console.

1. Add the Callback Class: Place the compiled custom callback class in the appropriate directory within the AM installation, usually under webapps/openam/WEB-INF/classes.
2. Configure in AM Console: Log in to the AM console, navigate to the authentication configuration, and add the custom callback to the authentication chain.

Advanced Extension Techniques

ForgeRock AM provides several advanced techniques for extending the functionality of custom callbacks. These techniques allow you to create more sophisticated and flexible authentication flows.

1. Using Scripting for Dynamic Callbacks

ForgeRock AM supports scripting languages like JavaScript and Groovy, which can be used to create dynamic callbacks without the need for compiling Java classes. This approach is particularly useful for rapid prototyping or when the custom logic is relatively simple.

Example: Using JavaScript for a Custom Callback

function handleCallback(context) {
    // Get the attribute name from the callback configuration
    var attributeName = context.getAttributeName();

    // Collect user input
    var userInput = context.getUserInput();

    // Validate the input
    if (userInput == null || userInput.isEmpty()) {
        throw new Error("The attribute " + attributeName + " cannot be empty.");
    }

    // Set the result
    var result = {
        success: true,
        resultData: userInput
    };

    return result;
}

2. Integrating with External Systems

Custom callbacks can be extended to integrate with external systems, such as databases, web services, or legacy systems. This allows you to leverage existing infrastructure and extend the functionality of ForgeRock AM.

Example: Integrating with an External Database

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;

public class DatabaseValidationCallback extends CustomUserAttributeCallback {

    private String jdbcUrl;
    private String username;
    private String password;

    public DatabaseValidationCallback(String attributeName, String jdbcUrl, String username, String password) {
        super(attributeName);
        this.jdbcUrl = jdbcUrl;
        this.username = username;
        this.password = password;
    }

    @Override
    public CustomCallbackResult process(CustomCallbackContext context) throws CustomCallbackException {
        String userInput = context.getUserInput();

        try (Connection conn = DriverManager.getConnection(jdbcUrl, username, password)) {
            String query = "SELECT value FROM user_attributes WHERE attribute_name = ? AND user_id = ?";
            PreparedStatement pstmt = conn.prepareStatement(query);
            pstmt.setString(1, getAttributeName());
            pstmt.setString(2, context.getUserId());

            ResultSet rs = pstmt.executeQuery();
            if (rs.next()) {
                String storedValue = rs.getString("value");
                if (!storedValue.equals(userInput)) {
                    throw new CustomCallbackException("The provided attribute value does not match the stored value.");
                }
            } else {
                throw new CustomCallbackException("No attribute found for the given user.");
            }
        } catch (SQLException e) {
            throw new CustomCallbackException("Database error occurred.", e);
        }

        return super.process(context);
    }
}

Explanation

• Database Connection: The callback establishes a connection to an external database using JDBC.
• Query Execution: It executes a query to retrieve the stored attribute value for the current user.
• Validation: The callback compares the provided user input with the stored value and throws an exception if they do not match.

3. Implementing Stateful Callbacks

In some cases, you may need to implement stateful callbacks that maintain state across multiple executions. This can be useful for multi-step authentication flows or for collecting information over time.

Example: Stateful Callback for Multi-Step Authentication

public class MultiStepAuthenticationCallback implements CustomCallback {

    private static final String STEP_ATTRIBUTE = "multiStepAuthStep";
    private static final int INITIAL_STEP = 1;
    private static final int FINAL_STEP = 2;

    @Override
    public void init(CustomCallbackContext context) throws CustomCallbackException {
        // Initialize the step counter
        context.setSessionAttribute(STEP_ATTRIBUTE, INITIAL_STEP);
    }

    @Override
    public CustomCallbackResult process(CustomCallbackContext context) throws CustomCallbackException {
        int currentStep = (int) context.getSessionAttribute(STEP_ATTRIBUTE);

        switch (currentStep) {
            case INITIAL_STEP:
                // Collect the first piece of information
                String firstInput = context.getUserInput();
                if (firstInput == null || firstInput.isEmpty()) {
                    throw new CustomCallbackException("First input cannot be empty.");
                }
                context.setSessionAttribute("firstInput", firstInput);

                // Move to the next step
                context.setSessionAttribute(STEP_ATTRIBUTE, FINAL_STEP);
                context.setCallbackHelpText("Please provide the second piece of information.");

                return new CustomCallbackResult(true, null);
            case FINAL_STEP:
                // Collect the second piece of information
                String secondInput = context.getUserInput();
                if (secondInput == null || secondInput.isEmpty()) {
                    throw new CustomCallbackException("Second input cannot be empty.");
                }

                // Validate both inputs
                String firstValue = (String) context.getSessionAttribute("firstInput");
                if (!isValidCombination(firstValue, secondInput)) {
                    throw new CustomCallbackException("Invalid combination of inputs.");
                }

                return new CustomCallbackResult(true, null);
            default:
                throw new CustomCallbackException("Invalid step encountered.");
        }
    }

    @Override
    public void cleanup(CustomCallbackContext context) throws CustomCallbackException {
        // Cleanup session attributes
        context.removeSessionAttribute(STEP_ATTRIBUTE);
        context.removeSessionAttribute("firstInput");
    }

    private boolean isValidCombination(String firstValue, String secondValue) {
        // Implement your validation logic here
        return firstValue.equals(secondValue);
    }
}

Explanation

• State Management: The callback uses session attributes to maintain state across multiple executions. The STEP_ATTRIBUTE tracks the current step in the authentication flow.
• Multi-Step Flow: The process method handles different steps based on the current step value. In the initial step, it collects the first piece of information and moves to the next step. In the final step, it validates both inputs.
• Validation: The isValidCombination method contains the logic to validate the combination of inputs. This can be customized based on specific business requirements.

Best Practices for Implementing Custom Callbacks

When implementing custom callbacks in ForgeRock AM, it’s important to follow best practices to ensure robustness, maintainability, and compatibility with future updates.

1. Keep It Simple and Modular

Avoid implementing overly complex logic within a single callback. Instead, break down the functionality into smaller, modular components. This makes the code easier to understand, test, and maintain.

2. Handle Exceptions Gracefully

Custom callbacks should handle exceptions gracefully and provide meaningful error messages. This helps in diagnosing issues during development and in production environments.

3. Use Logging Effectively

Implement logging in your custom callbacks to track the execution flow and debug issues. Use appropriate log levels and avoid logging sensitive information.

4. Test Thoroughly

Thoroughly test your custom callbacks in a controlled