Implementing the BFF Pattern with Spring Boot and Azure: Securing JWT Tokens in SPA Applications

Introduction

When building a Single Page Application (SPA) with a backend service, security is a paramount concern. One critical aspect is ensuring that the JSON Web Token (JWT) is not exposed to the public client. In this blog post, we will explore how to achieve this using the Backend for Frontend (BFF) pattern with a Spring Boot backend and an Azure environment.

Understanding the BFF Pattern

The Backend for Frontend (BFF) pattern involves creating a backend service specifically tailored to serve a particular frontend. This backend acts as an intermediary between the SPA and the resource servers, handling authentication and storing the JWT token securely.

Steps to Implement the BFF Pattern

1. Authentication Flow

User Login: The user logs in through the SPA.
Token Exchange: The SPA sends the user credentials to the BFF.
Token Storage: The BFF validates the credentials, obtains a JWT token from the authentication server, and stores it securely.
Session Management: The BFF creates a session for the user and issues a secure cookie to the SPA.

2. Secure Cookie Configuration

HttpOnly Cookies: Ensure that the cookies are marked as HttpOnly to prevent client-side JavaScript from accessing them.
Secure Cookies: Use the Secure flag to ensure that cookies are only sent over HTTPS.
SameSite Attribute: Set the SameSite attribute to Strict or Lax to prevent cross-site request forgery (CSRF) attacks.

3. SPA Communication

API Requests: The SPA communicates with the BFF using the secure cookie for authentication.
Token Usage: The BFF uses the stored JWT token to authenticate requests to resource servers on behalf of the SPA.

Hosting the SPA

You have a couple of options for hosting the SPA:

Azure Blob Storage: Host the SPA as a static website in Azure Blob Storage. This method is cost-effective and straightforward.
Static Web Apps: Use Azure Static Web Apps, which provide hosting for static websites with serverless APIs, seamless authentication, and global distribution.

Code Implementation

Below is an example of how to configure a Spring Boot application to implement the BFF pattern:

@Configuration
public class SecurityConfig extends WebSecurityConfigurerAdapter {

    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http
            .csrf().disable()
            .authorizeRequests()
            .antMatchers("/api/**").authenticated()
            .and()
            .oauth2Login()
            .loginPage("/login")
            .and()
            .sessionManagement()
            .sessionCreationPolicy(SessionCreationPolicy.IF_REQUIRED)
            .and()
            .addFilter(new JwtAuthenticationFilter(authenticationManager()));
    }
}

public class JwtAuthenticationFilter extends OncePerRequestFilter {

    private final AuthenticationManager authenticationManager;

    public JwtAuthenticationFilter(AuthenticationManager authenticationManager) {
        this.authenticationManager = authenticationManager;
    }

    @Override
    protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain chain)
            throws ServletException, IOException {
        String token = getJwtFromCookie(request);

        if (token != null) {
            try {
                Authentication auth = getAuthentication(token);
                SecurityContextHolder.getContext().setAuthentication(auth);
            } catch (Exception e) {
                SecurityContextHolder.clearContext();
            }
        }

        chain.doFilter(request, response);
    }

    private String getJwtFromCookie(HttpServletRequest request) {
        Cookie[] cookies = request.getCookies();
        if (cookies != null) {
            for (Cookie cookie : cookies) {
                if ("JWT-TOKEN".equals(cookie.getName())) {
                    return cookie.getValue();
                }
            }
        }
        return null;
    }

    private Authentication getAuthentication(String token) {
        // Validate and parse the JWT token
        // Return an Authentication object
    }
}

Conclusion

By implementing the BFF pattern, you can effectively secure your JWT tokens and prevent them from being exposed to public clients. Hosting the SPA in Azure Blob Storage or using Azure Static Web Apps can provide a scalable and secure solution. This approach not only enhances security but also simplifies the management of authentication and session handling in your application.

Keywords

JWT token security
BFF pattern with Spring Boot
Secure SPA with Spring Boot backend
Hosting SPA in Azure
Azure Static Web Apps
Secure cookie configuration
Prevent JWT exposure

Feel free to ask if you have any questions or need further assistance!