Spring Security Basic Guide

Spring Security is one of the most robust and versatile modules of the Spring framework, designed to provide complete security for Java applications. With it, you can configure authentication, authorization and other security practices.
To better understand Spring Security, let's explore the concepts of authentication and authorization, as well as common annotations and practices, such as using tokens to protect data and user interactions.
Security in Spring Security begins with the concepts of authentication and authorization, which have distinct functions:

Authentication: This is the process of verifying the user's identity. Typically, authentication requires the user to provide credentials, such as a login and password, which are compared to information stored in a database or other authentication system. Thus, the system guarantees that whoever is trying to access the system is who they say they are. An example is a stock application, where a user needs to authenticate before viewing or registering items.
Authorization: After authentication, the next step is to check whether the user has permission to access certain resources. In the example of the inventory system, let's imagine that there are different roles, such as ADMIN and EMPLOYEE. Only a user with the ADMIN role can add items to the inventory, while the EMPLOYEE can, for example, only view items. If João, who has the EMPLOYEE role, tries to add an item to the inventory, this action will be blocked.

Spring Security offers several annotations to simplify the implementation of security rules. Some of the most used are:

@PreAuthorize: Performs permissions check before the method is executed. For example:

@PreAuthorize("hasRole('ADMIN')")
public void addStockItem() {
// Code to add item
}
This method will only be executed if the user has the role "ADMIN".

@Secured: Similar to @PreAuthorize, but with a more direct configuration, @Secured allows you to specify which roles can access a given method.

@Secured({"ROLE_ADMIN", "ROLE_USER"})
public void acessRestrictedMethod() {
// Code for restricted method
}
In this case, the method is only accessible to users with roles "ROLE_ADMIN" or "ROLE_USER".

In modern applications, especially in REST APIs, the use of token-based authentication is very common. Spring Security facilitates integration with JWT, a secure and lightweight standard that allows the creation of stateless sessions in which the token is sent with each request.
When logging in, the user receives a JWT token signed by the server, which is stored on the client and sent in the next requests. Spring Security validates the token, verifying the user's permissions and authenticity before allowing access to the requested resource.

In addition to authentication and authorization, Spring Security offers additional features to further protect applications:

Protection Against CSRF Attacks: Cross-Site Request Forgery (CSRF) is a type of attack that Spring Security helps mitigate by generating specific tokens for each user session, preventing malicious requests from being accepted.
Password Encryption: Spring Security provides classes and configurations to encrypt passwords before storing them, preventing them from being stored in plain text, which is an insecure practice.
Security Filters: Uses a chain of filters that intercept HTTP requests to apply security checks, such as user authentication and token validation.

Spring Security is a complete and robust tool that raises the security level of Java applications, integrating authentication, authorization and protection against common attacks in a single framework. With features such as annotation support (@PreAuthorize, @Secured, among others), JWT token authentication and CSRF protection, Spring Security offers suitable solutions for applications of any size.

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