Springboot Security

# Spring Boot Security Review

Use when adding auth, handling input, creating endpoints, or dealing with secrets.

## When to Activate

- Adding authentication (JWT, OAuth2, session-based)
- Implementing authorization (@PreAuthorize, role-based access)
- Validating user input (Bean Validation, custom validators)
- Configuring CORS, CSRF, or security headers
- Managing secrets (Vault, environment variables)
- Adding rate limiting or brute-force protection
- Scanning dependencies for CVEs

## Authentication

- Prefer stateless JWT or opaque tokens with revocation list
- Use `httpOnly`, `Secure`, `SameSite=Strict` cookies for sessions
- Validate tokens with `OncePerRequestFilter` or resource server

```java
@Component
public class JwtAuthFilter extends OncePerRequestFilter {
  private final JwtService jwtService;

  public JwtAuthFilter(JwtService jwtService) {
    this.jwtService = jwtService;
  }

  @Override
  protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response,
      FilterChain chain) throws ServletException, IOException {
    String header = request.getHeader(HttpHeaders.AUTHORIZATION);
    if (header != null && header.startsWith("Bearer ")) {
      String token = header.substring(7);
      Authentication auth = jwtService.authenticate(token);
      SecurityContextHolder.getContext().setAuthentication(auth);
    }
    chain.doFilter(request, response);
  }
}
```

## Authorization

- Enable method security: `@EnableMethodSecurity`
- Use `@PreAuthorize("hasRole('ADMIN')")` or `@PreAuthorize("@authz.canEdit(#id)")`
- Deny by default; expose only required scopes

```java
@RestController
@RequestMapping("/api/admin")
public class AdminController {

  @PreAuthorize("hasRole('ADMIN')")
  @GetMapping("/users")
  public List<UserDto> listUsers() {
    return userService.findAll();
  }

  @PreAuthorize("@authz.isOwner(#id, authentication)")
  @DeleteMapping("/users/{id}")
  public ResponseEntity<Void> deleteUser(@PathVariable Long id) {
    userService.delete(id);
    return ResponseEntity.noContent().build();
  }
}
```

## Input Validation

- Use Bean Validation with `@Valid` on controllers
- Apply constraints on DTOs: `@NotBlank`, `@Email`, `@Size`, custom validators
- Sanitize any HTML with a whitelist before rendering

```java
// BAD: No validation
@PostMapping("/users")
public User createUser(@RequestBody UserDto dto) {
  return userService.create(dto);
}

// GOOD: Validated DTO
public record CreateUserDto(
    @NotBlank @Size(max = 100) String name,
    @NotBlank @Email String email,
    @NotNull @Min(0) @Max(150) Integer age
) {}

@PostMapping("/users")
public ResponseEntity<UserDto> createUser(@Valid @RequestBody CreateUserDto dto) {
  return ResponseEntity.status(HttpStatus.CREATED)
      .body(userService.create(dto));
}
```

## SQL Injection Prevention

- Use Spring Data repositories or parameterized queries
- For native queries, use `:param` bindings; never concatenate strings

```java
// BAD: String concatenation in native query
@Query(value = "SELECT * FROM users WHERE name = '" + name + "'", nativeQuery = true)

// GOOD: Parameterized native query
@Query(value = "SELECT * FROM users WHERE name = :name", nativeQuery = true)
List<User> findByName(@Param("name") String name);

// GOOD: Spring Data derived query (auto-parameterized)
List<User> findByEmailAndActiveTrue(String email);
```

## Password Encoding

- Always hash passwords with BCrypt or Argon2 — never store plaintext
- Use `PasswordEncoder` bean, not manual hashing

```java
@Bean
public PasswordEncoder passwordEncoder() {
  return new BCryptPasswordEncoder(12); // cost factor 12
}

// In service
public User register(CreateUserDto dto) {
  String hashedPassword = passwordEncoder.encode(dto.password());
  return userRe