Elevate Your Security Game: Spring Security’s Lambda DSL Unleashed
Tags: springsecurity, spring, java
Published: 2023-09-09 02:30:08

## Introduction
In the realm of web application security, Spring Security has long been a powerhouse, offering robust features and a flexible configuration system. With the release of Spring Security 5.2, a new configuration approach known as the Lambda DSL was introduced, bringing increased flexibility and readability to the security configuration process. This article dives into the Lambda DSL for Spring Security, comparing it with the traditional configuration style, highlighting its benefits, and providing insights into its goals.

## Overview of Lambda DSL
The Lambda DSL is an alternative way to configure HTTP security in Spring applications. It allows developers to define security rules and policies using lambda expressions, making the configuration process more concise and readable.

Before we delve into the Lambda DSL, it’s important to note that the conventional configuration style is still perfectly valid and supported. The introduction of lambdas is intended to enhance flexibility rather than replace the existing configuration method. You can choose to use lambdas based on your preference and project requirements.

## Configuration using Lambdas
Let’s start by looking at how you can configure Spring Security using lambdas:

```
@EnableWebSecurity
public class SecurityConfig extends WebSecurityConfigurerAdapter {

    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http
            .authorizeRequests(authorizeRequests ->
                authorizeRequests
                    .antMatchers("/blog/**").permitAll()
                    .anyRequest().authenticated()
            )
            .formLogin(formLogin ->
                formLogin
                    .loginPage("/login")
                    .permitAll()
            )
            .rememberMe(withDefaults());
    }
}
```


## Equivalent Configuration without Lambdas
To provide a clear comparison, here’s the equivalent configuration using the traditional style:

```
@EnableWebSecurity
public class SecurityConfig extends WebSecurityConfigurerAdapter {

    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http
            .authorizeRequests()
                .antMatchers("/blog/**").permitAll()
                .anyRequest().authenticated()
                .and()
            .formLogin()
                .loginPage("/login")
                .permitAll()
                .and()
            .rememberMe();
    }
}

```

## Lambda DSL Configuration Tips
When comparing the two samples above, you’ll notice some key differences and benefits when using the Lambda DSL:

- **No Chaining with .and():** In the Lambda DSL, there's no need to chain configuration options using the .and() method. After calling the lambda method, the HttpSecurity instance is automatically returned for further configuration.

- **withDefaults() Shortcut:** The withDefaults() function is a convenient way to enable a security feature using the defaults provided by Spring Security. It essentially represents an empty lambda expression (it -> {}).
These differences contribute to a more concise and readable configuration experience.

## WebFlux Security
The Lambda DSL is not limited to traditional Spring MVC applications; you can also configure WebFlux security with lambdas. Here’s an example configuration using lambdas for WebFlux security:

```
@EnableWebFluxSecurity
public class SecurityConfig {

    @Bean
    SecurityWebFilterChain springSecurityFilterChain(ServerHttpSecurity http) {
        http
            .authorizeExchange(exchanges ->
                exchanges
                    .pathMatchers("/blog/**").permitAll()
                    .anyExchange().authenticated()
            )
            .httpBasic(withDefaults())
            .formLogin(formLogin ->
                formLogin
                    .loginPage("/login")
            );
        return http.build();
    }
}
```

## Goals of the Lambda DSL

The Lambda DSL for Spring Security was designed with several key goals in mind:

1. **Automatic Indentation:** By using lambda expressions, the configuration code becomes inherently more readable, reducing the need for excessive indentation and improving overall code quality.
2. **No Chaining with .and():** One of the notable benefits of the Lambda DSL is the elimination of explicit .and() chaining, resulting in cleaner and more intuitive configuration code.
3. **Consistency Across Spring DSLs:** The Lambda DSL adopts a configuration style that aligns with other Spring DSLs, such as Spring Integration and Spring Cloud Gateway. This consistency provides a familiar experience for developers familiar with the broader Spring ecosystem.

## Migration to Lambda DSL
If you’re considering migrating your existing Spring Security configuration to the Lambda DSL, here are some steps to help you get started:

1. **Review Existing Configuration:** Begin by reviewing your current Spring Security configuration. Understand the existing security rules and policies.
2. **Create Lambda Expressions:** Identify areas where you can use lambda expressions to replace the existing configuration. Focus on authorization rules, login configurations, and other security-related settings.
3. **Refactor Gradually:** Consider refactoring your configuration gradually. You don’t need to rewrite the entire configuration at once. Start by converting specific sections to lambdas and test them thoroughly.
4. **Testing:** Rigorous testing is crucial when migrating to the Lambda DSL. Ensure that your security rules and policies are still effective after the migration.
5. **Documentation:** Update your project’s documentation to reflect the changes made during the migration. Document the use of lambdas and their benefits for your team.

## Conclusion
Spring Security’s Lambda DSL is a valuable addition to the toolkit of Spring developers, offering a more concise and readable way to configure security in your applications. While the traditional configuration style remains robust and widely used, the Lambda DSL presents an optional, streamlined alternative. Whether you choose to adopt it or stick with the conventional approach, Spring Security continues to empower you with powerful security features and flexible configuration options to protect your applications. The Lambda DSL is just one more tool at your disposal for crafting secure and reliable software.

## Reference:
https://spring.io/blog/2019/11/21/spring-security-lambda-dsl