Material complementar:

• Conteúdo no YouTube: Acesse em breve
• Conteúdo no GitHub: Acesse

Conceito:

JWT (JSON Web Token) é padrão (RFC 7519) de token stateless (geralmente do tipo Bearer token) usado para autenticação/autorização na troca de informações entre cliente e servidor (HTTP request/response) de forma segura (geralmente em conjunto com protocolo OAuth2), assinadas com Message Authentication Code (HMAC). Access Token é token de curta duração com expiração, usado para acessar recursos protegidos da API, enviado em cada request no header Authorization. Refresh Token é token de longa duração de expiração, usado apenas para gerar novos access tokens. Sua estrutura consiste em header (tipo de token e algoritmo de assinatura), payload (dados claims, como subject, issuedAt, expiration) e signature (assinatura criptográfica do header e payload usando secret key). JWT amplamente utilizado em sistemas web RESTful (arquitetura REST) stateless (sem manter estado no servidor), com funções encoder (criação) e decoder (leitura).

Fluxo do projeto abaixo:

Cliente acessa /api/auth/login, recebe tokens, depois envia access token em /api/hello. Filtro valida token, liberando acesso ao controller.

1. SecurityConfig.kt define regras de segurança, libera /api/auth/** e protege demais endpoints, além de registrar filtro JWT;
2. JwtAuthenticationFilter.kt intercepta todas requisições, lê header Authorization, valida token e define usuário no SecurityContext;
3. JwtService.kt gera access e refresh token, e extrai username do token;
4. LoginRequest.kt define formato da requisição de login com username e password;
5. TokenResponse.kt define formato da resposta contendo accessToken e refreshToken;
6. AuthController.kt recebe requisição /api/auth/login, valida credenciais (mock), invoca JwtService e retorna tokens;
7. HelloController.kt expõe endpoint /api/hello que está protegido pelo Spring Security e exige token válido;
8. HelloResponse.kt define formato de resposta do endpoint protegido ou público de teste.

Implementação:

Projeto Spring Boot Kotlin API REST para implementação de JWT.

1. Criar projeto em https://start.spring.io
   • Project: Gradle - Kotlin
   • Language: Kotlin
   • Spring Boot: 4.0.6
   • Project Metadata:
     • Group: com.example
     • Artifact: myjwt
     • Package name: com.example.myjwt
     • Packaging: Jar
     • Configuration: properties
     • Java: 21
   • Generate
     • Extrair e abrir projeto no editor (IntelliJ IDEA)
2. No projeto, criar pacotes:

   
   com.example.myjwt.controller
   com.example.myjwt.dto
   com.example.myjwt.security
   

3. Conteúdo de 'build.gradle.kts':

   
   plugins {
   	kotlin("jvm") version "2.2.21"
   	kotlin("plugin.spring") version "2.2.21"
   	id("org.springframework.boot") version "4.0.6"
   	id("io.spring.dependency-management") version "1.1.7"
   }
   
   group = "com.example"
   version = "0.0.1-SNAPSHOT"
   
   java {
   	toolchain {
   		languageVersion = JavaLanguageVersion.of(21)
   	}
   }
   
   repositories {
   	mavenCentral()
   }
   
   dependencies {
   	implementation("org.springframework.boot:spring-boot-starter-web")
   	implementation("com.fasterxml.jackson.module:jackson-module-kotlin")
   	implementation("org.jetbrains.kotlin:kotlin-reflect")
   	implementation("org.springframework.boot:spring-boot-starter-security")
   	developmentOnly("org.springframework.boot:spring-boot-devtools")
   	testImplementation("org.springframework.boot:spring-boot-starter-test")
   	implementation("io.jsonwebtoken:jjwt-api:0.12.6")
   	runtimeOnly("io.jsonwebtoken:jjwt-impl:0.12.6")
   	runtimeOnly("io.jsonwebtoken:jjwt-jackson:0.12.6")
   }
   
   kotlin {
   	compilerOptions {
   		freeCompilerArgs.addAll("-Xjsr305=strict")
   	}
   }
   
   tasks.withType<Test> {
   	useJUnitPlatform()
   }
   

4. No pacote 'myjwt.dto', criar DTO 'HelloResponse.kt':

   
   package com.example.myjwt.dto
   
   data class HelloResponse(
       val message: String,
       val status: String
   )
   

5. No pacote 'myjwt.controller', criar Controller 'HelloController.kt':

   
   package com.example.myjwt.controller
   
   import com.example.myjwt.dto.HelloResponse
   import org.springframework.web.bind.annotation.GetMapping
   import org.springframework.web.bind.annotation.RequestMapping
   import org.springframework.web.bind.annotation.RestController
   
   @RestController
   @RequestMapping("/api")
   class HelloController {
   
       @GetMapping("/hello")
       fun hello(): HelloResponse {
           return HelloResponse(
               message = "API REST funcionando!",
               status = "OK"
           )
       }
   }
   

6. Em 'build.gradle.kts', comentar implementation de segurança:

   
   '//implementation("org.springframework.boot:spring-boot-starter-security")'
   

7. Construir projeto: ./gradlew clean build
8. Executar projeto: ./gradlew bootRun
   • Acessar no browser (GET): http://localhost:8080/api/hello
     • Response com sucesso (200 OK)
9. Em 'build.gradle.kts', remover comentário implementation de segurança:

   
   'implementation("org.springframework.boot:spring-boot-starter-security")'
   

10. No pacote 'myjwt.security', criar Service 'JwtService.kt':

    
    package com.example.myjwt.security
    
    import io.jsonwebtoken.Jwts
    import io.jsonwebtoken.security.Keys
    import org.springframework.stereotype.Service
    import java.util.*
    import javax.crypto.SecretKey
    
    @Service
    class JwtService {
    
        private val secretKey: SecretKey = Keys.hmacShaKeyFor(
            "my-super-secret-key-my-super-secret-key".toByteArray()
        )
    
        private val accessExpirationMs = 1000 * 60 * 5L
        private val refreshExpirationMs = 1000 * 60 * 60 * 24L
    
        fun generateAccessToken(username: String): String {
            return Jwts.builder()
                .subject(username)
                .issuedAt(Date())
                .expiration(Date(System.currentTimeMillis() + accessExpirationMs))
                .signWith(secretKey)
                .compact()
        }
    
        fun generateRefreshToken(username: String): String {
            return Jwts.builder()
                .subject(username)
                .issuedAt(Date())
                .expiration(Date(System.currentTimeMillis() + refreshExpirationMs))
                .claim("type", "refresh")
                .signWith(secretKey)
                .compact()
        }
    
        fun extractUsername(token: String): String {
            return Jwts.parser()
                .verifyWith(secretKey)
                .build()
                .parseSignedClaims(token)
                .payload
                .subject
        }
    }
    

11. No pacote 'myjwt.security', criar classe 'SecurityConfig.kt':

    
    package com.example.myjwt.security
    
    import jakarta.servlet.http.HttpServletResponse
    import org.springframework.context.annotation.Bean
    import org.springframework.context.annotation.Configuration
    import org.springframework.security.config.annotation.web.builders.HttpSecurity
    import org.springframework.security.config.http.SessionCreationPolicy
    import org.springframework.security.web.SecurityFilterChain
    import org.springframework.security.web.authentication.UsernamePasswordAuthenticationFilter
    
    @Configuration
    class SecurityConfig(
        private val jwtAuthenticationFilter: JwtAuthenticationFilter
    ) {
    
        @Bean
        fun securityFilterChain(http: HttpSecurity): SecurityFilterChain {
    
            http
                .csrf { it.disable() }
                .formLogin { it.disable() }
                .httpBasic { it.disable() }
                
                .exceptionHandling {
                    it.authenticationEntryPoint { _, response, _ ->
                        response.sendError(HttpServletResponse.SC_UNAUTHORIZED)
                    }
                }
    
                .sessionManagement {
                    it.sessionCreationPolicy(SessionCreationPolicy.STATELESS)
                }
    
                .authorizeHttpRequests {
                    it
                        .requestMatchers("/api/auth/**").permitAll()
                        .anyRequest().authenticated()
                }
    
                .addFilterBefore(
                    jwtAuthenticationFilter,
                    UsernamePasswordAuthenticationFilter::class.java
                )
    
            return http.build()
        }
    }
    

12. No pacote 'myjwt.security', criar classe de filtro 'JwtAuthenticationFilter.kt':

    
    package com.example.myjwt.security
    import jakarta.servlet.FilterChain
    import jakarta.servlet.http.HttpServletRequest
    import jakarta.servlet.http.HttpServletResponse
    import org.springframework.security.authentication.UsernamePasswordAuthenticationToken
    import org.springframework.security.core.context.SecurityContextHolder
    import org.springframework.security.core.userdetails.User
    import org.springframework.stereotype.Component
    import org.springframework.web.filter.OncePerRequestFilter
    
    @Component
    class JwtAuthenticationFilter(
        private val jwtService: JwtService
    ) : OncePerRequestFilter() {
    
        override fun doFilterInternal(
            request: HttpServletRequest,
            response: HttpServletResponse,
            filterChain: FilterChain
        ) {
            val authHeader = request.getHeader("Authorization")
            
            if (authHeader == null || !authHeader.startsWith("Bearer ")) {
                filterChain.doFilter(request, response)
                return
            }
    
            val token = authHeader.substring(7)
    
            try {
                val username = jwtService.extractUsername(token)
                
                val auth = UsernamePasswordAuthenticationToken(
                    User(username, "", emptyList()),
                    null,
                    emptyList()
                )
    
                SecurityContextHolder.getContext().authentication = auth
    
            } catch (e: Exception) {
                SecurityContextHolder.clearContext()
            }
    
            filterChain.doFilter(request, response)
        }
    }
    

13. No pacote 'myjwt.dto', criar DTO 'LoginRequest.kt':

    
    package com.example.myjwt.dto
    
    data class LoginRequest(
        val username: String,
        val password: String
    )
    

14. No pacote 'myjwt.dto', criar DTO 'TokenResponse.kt':

    
    package com.example.myjwt.dto
    
    data class TokenResponse(
        val accessToken: String,
        val refreshToken: String
    )
    

15. No pacote 'myjwt.controller', criar Controller 'AuthController.kt':

    
    package com.example.myjwt.controller
    
    import com.example.myjwt.dto.LoginRequest
    import com.example.myjwt.dto.TokenResponse
    import com.example.myjwt.security.JwtService
    import org.springframework.web.bind.annotation.*
    
    @RestController
    @RequestMapping("/api/auth")
    class AuthController(
        private val jwtService: JwtService
    ) {
    
        @PostMapping("/login")
        fun login(@RequestBody request: LoginRequest): TokenResponse {
            
            if (request.username != "admin" || request.password != "123") {
                throw RuntimeException("Invalid credentials")
            }
            
            val accessToken = jwtService.generateAccessToken(request.username)
            val refreshToken = jwtService.generateRefreshToken(request.username)
            
            return TokenResponse(
                accessToken = accessToken,
                refreshToken = refreshToken
            )
        }
    }
    

16. Construir projeto: ./gradlew clean build
17. Executar projeto: ./gradlew bootRun
18. Testar request sem autenticação: GET http://localhost:8080/api/hello
    • Response com erro (401 Unauthorized)
19. Criar token JWT (copiar token gerado): POST http://localhost:8080/api/auth/login

    
    {
      "username": "admin",
      "password": "123"
    }
    

20. Testar request com autenticação: GET http://localhost:8080/api/hello (Authorization: Bearer token)
    • Response com sucesso (200 OK)