Introduction to Spring Security

Table of Contents

1. What is Spring Security?
2. Core Features of Spring Security
3. How Spring Security Works
4. Spring Security Architecture
5. Adding Spring Security to a Spring Boot Application
6. Default Behavior and Auto-Configuration
7. Summary

1. What is Spring Security?

Spring Security is a powerful and customizable authentication and access control framework for Java applications, especially those built using the Spring framework. It is the de facto standard for securing Spring-based applications.

Spring Security offers comprehensive security services for:

• Authentication – verifying the identity of users.
• Authorization – controlling access to resources based on roles/permissions.

It supports a wide range of security features including form-based login, OAuth2, JWT, LDAP, method-level security, and much more.

2. Core Features of Spring Security

Spring Security comes with a rich set of security features:

• Authentication and Authorization: Built-in support for user login and role-based access control.
• Password Encoding: Uses secure hashing algorithms (like BCrypt) to store passwords.
• Security Headers: Helps protect against attacks such as XSS, clickjacking, etc.
• CSRF Protection: Cross-Site Request Forgery protection is enabled by default.
• Session Management: Controls concurrent sessions and session invalidation.
• Method-Level Security: Allows securing methods using annotations such as @PreAuthorize, @Secured.
• Integration: Easily integrates with OAuth2, LDAP, SAML, and custom authentication providers.

3. How Spring Security Works

Spring Security works by configuring a filter chain that intercepts incoming HTTP requests and processes them through various security filters.

Basic Flow:

1. A user sends a request to a secured resource.
2. The request hits the Security Filter Chain, which checks if the resource requires authentication.
3. If yes, Spring Security checks whether the user is authenticated and has the necessary authority.
4. If authenticated and authorized, access is granted. If not, a suitable error (like 401 or 403) is returned.

The filters in the chain can handle:

• Logging in/out
• Validating session or tokens
• CSRF validation
• Applying security headers

4. Spring Security Architecture

Key components in Spring Security:

• SecurityFilterChain: Central component for applying security filters to incoming requests.
• AuthenticationManager: Responsible for processing authentication requests.
• UserDetailsService: Interface to fetch user-specific data.
• GrantedAuthority: Represents the role or privilege assigned to a user.
• SecurityContext: Holds the currently authenticated user’s details in a thread-local storage.
• PasswordEncoder: Used to hash passwords before storing and comparing them.

5. Adding Spring Security to a Spring Boot Application

Step 1: Add Dependency

In pom.xml:

xmlCopyEdit<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-security</artifactId>
</dependency>

Or for Gradle:

groovyCopyEditimplementation 'org.springframework.boot:spring-boot-starter-security'

Step 2: Default Behavior

Once the dependency is added, Spring Boot auto-configures basic security:

• All endpoints are secured by default.
• A login form is available at /login.
• A default in-memory user with a generated password is created.

On application startup, a password will be printed in the logs:

pgsqlCopyEditUsing generated security password: 9d5b6142-XXXX-XXXX

You can use this to log in with the default user user.

6. Default Behavior and Auto-Configuration

When Spring Security is included:

• All HTTP endpoints require authentication.
• A login page is auto-generated at /login.
• HTTP Basic and Form-based authentication are enabled.
• CSRF protection is enabled.
• Static resources (like CSS, JS) are allowed by default.

You can customize this behavior using a configuration class:

javaCopyEdit@Configuration
public class SecurityConfig {

    @Bean
    public SecurityFilterChain filterChain(HttpSecurity http) throws Exception {
        http
            .authorizeHttpRequests()
            .requestMatchers("/public/**").permitAll()
            .anyRequest().authenticated()
            .and()
            .formLogin();
        return http.build();
    }
}

7. Summary

Spring Security is a full-featured, highly customizable framework for securing Java applications. Its plug-and-play integration with Spring Boot makes it easy to set up authentication and authorization for your REST APIs or web applications.

Key Points:

• It provides robust security features including CSRF, headers, sessions, and method-level access control.
• Security is applied through a filter chain that intercepts and processes every request.
• Once integrated, all endpoints are protected by default until explicitly configured.

In upcoming modules, we will cover:

• Custom user details and authentication providers
• JWT-based security
• Role-based access control
• Method-level and endpoint-level security
• Integration with Spring Boot APIs

This foundational understanding is essential as we dive deeper into securing real-world applications using Spring Security.