カスタムJWTフィルターの実装
カスタム`OncePerRequestFilter`を構築し、リクエストをインターセプトしてJWTを抽出し、ユーザーを認証します。
「カスタムJWTフィルターの実装」はCoddyKit上の無料Spring Security 6 & JWT Authenticationレッスンです。 これはレッスン2/4です。 下記で完全なレッスンを無料で読むことができます。その後、ブラウザ内の組み込みコードエディタと24時間対応のAIチューターでハンズオン演習できます。 これはSpring Security 6 & JWT Authentication学習パスの一部であり、ウェブとCoddyKitアプリ全体で進捗が同期されます。 Spring Security 6 & JWT Authenticationコースには全4レッスンが含まれています。
このレッスンの一部はまだ翻訳されておらず、英語で表示されています。
Why a Custom JWT Filter?
When using JSON Web Tokens (JWTs) for authentication, Spring Security doesn't inherently know how to process them. This is where a custom filter comes in!
A custom JWT filter intercepts incoming requests to:
- Extract the JWT.
- Validate its authenticity and expiration.
- Inform Spring Security about the authenticated user.
The OncePerRequestFilter Base
For our custom JWT filter, we'll extend Spring's OncePerRequestFilter. This base class guarantees that your filter logic runs exactly once per HTTP request, preventing redundant processing.
- It simplifies filter implementation.
- Ensures efficiency for each request.
- It's ideal for authentication logic.
Basic Filter Structure
Every custom filter extending OncePerRequestFilter must override the doFilterInternal method. This is where our JWT processing logic will reside.
It provides access to the HttpServletRequest, HttpServletResponse, and the FilterChain to pass the request along.
import jakarta.servlet.FilterChain;
import jakarta.servlet.ServletException;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import org.springframework.web.filter.OncePerRequestFilter;
import java.io.IOException;
public class JwtAuthenticationFilter extends OncePerRequestFilter {
@Override
protected void doFilterInternal(
HttpServletRequest request,
HttpServletResponse response,
FilterChain filterChain
) throws ServletException, IOException {
// Our JWT logic will go here
filterChain.doFilter(request, response);
}
}Extracting the JWT
The first step in our filter is to extract the JWT from the incoming request. JWTs are typically sent in the Authorization header, prefixed with Bearer .
We need to check for this header and remove the 'Bearer ' part to get the raw token.
import jakarta.servlet.FilterChain;
import jakarta.servlet.ServletException;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import org.springframework.web.filter.OncePerRequestFilter;
import java.io.IOException;
public class JwtAuthenticationFilter extends OncePerRequestFilter {
@Override
protected void doFilterInternal(
HttpServletRequest request,
HttpServletResponse response,
FilterChain filterChain
) throws ServletException, IOException {
final String authHeader = request.getHeader("Authorization");
String jwt = null;
if (authHeader != null && authHeader.startsWith("Bearer ")) {
jwt = authHeader.substring(7); // Remove "Bearer " prefix
System.out.println("Extracted JWT: " + jwt.substring(0, 5) + "...");
} else {
System.out.println("No JWT found or invalid header.");
}
filterChain.doFilter(request, response);
}
}Validating & Parsing (Concept)
After extraction, the JWT must be validated. This involves:
- Signature verification: Ensuring the token hasn't been tampered with.
- Expiration check: Confirming the token is still valid.
- Claim extraction: Retrieving information like the username (subject) from the token's payload.
This validation is typically handled by a dedicated JwtService or similar utility, which our filter would use.
Loading User Details (Concept)
Once the JWT is validated and the username (or user ID) is extracted, the filter needs to load the user's specific details. This is usually done using Spring Security's UserDetailsService.
The UserDetailsService fetches the UserDetails object, which contains information like roles and authorities needed for authorization.
Setting Authentication Context
The final crucial step is to inform Spring Security that the user is authenticated for the current request. This is done by creating an Authentication object (e.g., UsernamePasswordAuthenticationToken) and setting it in the SecurityContextHolder.
Once set, Spring Security will recognize the user as authenticated for the duration of the request.
import org.springframework.security.authentication.UsernamePasswordAuthenticationToken;
import org.springframework.security.core.context.SecurityContextHolder;
import org.springframework.security.core.userdetails.User;
import org.springframework.security.core.userdetails.UserDetails;
import java.util.ArrayList;
public class Main {
public static void main(String[] args) {
// Simulate a UserDetails object loaded from DB
UserDetails userDetails = new User(
"exampleUser", "[PASSWORD_HASH]", new ArrayList<>()
);
// Create an Authentication token
UsernamePasswordAuthenticationToken authToken =
new UsernamePasswordAuthenticationToken(
userDetails, null, userDetails.getAuthorities()
);
// Set the Authentication in the SecurityContextHolder
SecurityContextHolder.getContext().setAuthentication(authToken);
System.out.println("Authentication set for: " +
SecurityContextHolder.getContext().getAuthentication().getName());
// Clear context after request (or for next test)
SecurityContextHolder.clearContext();
}
}Runnable Filter Logic Example
Let's see a simplified, runnable example that mimics the core logic of our custom JWT filter. It simulates extracting a token and setting authentication based on its presence.
This example uses mock components to show the flow without a full Spring Boot setup.
import java.util.HashMap;
import java.util.Map;
// Simulate Spring Security components needed for the filter logic
class MockSecurityContextHolder {
private static String authenticatedUser = null;
public static String getAuthentication() {
return authenticatedUser;
}
public static void setAuthentication(String user) {
authenticatedUser = user;
}
public static void clearContext() {
authenticatedUser = null;
}
}
public class Main {
// This method simulates the core logic of doFilterInternal
public static void simulateJwtFilter(Map<String, String> requestHeaders) {
System.out.println("--- Simulating JWT Filter Logic ---");
final String authHeader = requestHeaders.get("Authorization");
String jwt = null;
String username = null;
if (authHeader != null && authHeader.startsWith("Bearer ")) {
jwt = authHeader.substring(7);
// In a real app, this extracts username from JWT payload
username = "coddyuser"; // Simplified: assume "coddyuser" from a valid JWT
System.out.println("Filter: JWT found: " + jwt.substring(0, 5) + "...");
} else {
System.out.println("Filter: No JWT found or invalid header format.");
}
// Check if user is already authenticated
if (username != null && MockSecurityContextHolder.getAuthentication() == null) {
// Simulate JWT validation (signature, expiration, etc.)
boolean tokenValid = true; // Assume valid for this simple demo
if (tokenValid) {
// In a real filter, we'd load UserDetails and create an Authentication object
MockSecurityContextHolder.setAuthentication(username);
System.out.println("Filter: User '" + username + "' authenticated and context set.");
} else {
System.out.println("Filter: JWT validation failed.");
}
} else if (username != null && MockSecurityContextHolder.getAuthentication() != null) {
System.out.println("Filter: User '" + username + "' already authenticated for this request.");
}
// In a real filter, this would call filterChain.doFilter(...)
System.out.println("Filter: Request passed to next filter/handler.");
System.out.println("--- Filter Logic End ---");
}
public static void main(String[] args) {
// Scenario 1: Request with a valid JWT
Map<String, String> headers1 = new HashMap<>();
headers1.put("Authorization", "Bearer abc.def.ghi");
simulateJwtFilter(headers1);
System.out.println("Main: SecurityContext has authentication: " +
(MockSecurityContextHolder.getAuthentication() != null ? MockSecurityContextHolder.getAuthentication() : "None"));
MockSecurityContextHolder.clearContext(); // Clean up
System.out.println("\n");
// Scenario 2: Request without a JWT
Map<String, String> headers2 = new HashMap<>();
simulateJwtFilter(headers2);
System.out.println("Main: SecurityContext has authentication: " +
(MockSecurityContextHolder.getAuthentication() != null ? MockSecurityContextHolder.getAuthentication() : "None"));
MockSecurityContextHolder.clearContext(); // Clean up
}
}Integrating with Spring Security
After creating our JwtAuthenticationFilter, we need to register it with Spring Security's filter chain. This is typically done in your security configuration class (e.g., SecurityConfig) using HttpSecurity.
We use .addFilterBefore() to ensure our JWT filter runs before Spring Security's default authentication filters, like UsernamePasswordAuthenticationFilter.
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.annotation.web.configuration.EnableWebSecurity;
import org.springframework.security.web.SecurityFilterChain;
import org.springframework.security.web.authentication.UsernamePasswordAuthenticationFilter;
// Assuming JwtAuthenticationFilter is defined elsewhere
class JwtAuthenticationFilter extends OncePerRequestFilter {
@Override
protected void doFilterInternal(jakarta.servlet.http.HttpServletRequest request, jakarta.servlet.http.HttpServletResponse response, jakarta.servlet.FilterChain filterChain) throws jakarta.servlet.ServletException, java.io.IOException {
// Simplified for config demo
filterChain.doFilter(request, response);
}
}
@Configuration
@EnableWebSecurity
public class SecurityConfig {
private final JwtAuthenticationFilter jwtAuthFilter;
// Inject our custom JWT filter
public SecurityConfig(JwtAuthenticationFilter jwtAuthFilter) {
this.jwtAuthFilter = jwtAuthFilter;
}
@Bean
public SecurityFilterChain securityFilterChain(HttpSecurity http) throws Exception {
http
.csrf(csrf -> csrf.disable()) // Disable CSRF for stateless APIs
.authorizeHttpRequests(auth -> auth
.requestMatchers("/api/auth/**").permitAll() // Public endpoints
.anyRequest().authenticated() // Secure all other requests
)
// Add our custom JWT filter BEFORE the default UsernamePasswordAuthenticationFilter
.addFilterBefore(jwtAuthFilter, UsernamePasswordAuthenticationFilter.class);
return http.build();
}
}Filter Chain Challenge
Consider the JwtAuthenticationFilter we've discussed. What are its key responsibilities in the Spring Security filter chain when handling JWT-based authentication?
Lesson Recap: Custom JWT Filter
In this lesson, we explored how to build a custom OncePerRequestFilter to handle JWT authentication in Spring Security.
- We learned to extract JWTs from the
Authorizationheader. - We understood the conceptual steps of validating the token and loading user details.
- We saw how to authenticate the user by setting the
SecurityContextHolder. - Finally, we covered how to integrate this filter into Spring Security's filter chain using
HttpSecurity.addFilterBefore().
This custom filter is crucial for integrating JWTs seamlessly into your secure Spring Boot applications.
よくある質問
「カスタムJWTフィルターの実装」レッスンは無料ですか？
はい。「カスタムJWTフィルターの実装」の完全なテキストはこのウェブで無料で読めます。インタラクティブに演習し（組み込みコードエディタと24時間対応のAIチューター）、Spring Security 6 & JWT Authenticationコースの残りをアンロックするには、CoddyKit PROにアップグレードしてください。 Spring Security 6 & JWT Authenticationコースには全4レッスンが含まれています。
「カスタムJWTフィルターの実装」で何を学びますか？
カスタム`OncePerRequestFilter`を構築し、リクエストをインターセプトしてJWTを抽出し、ユーザーを認証します。 ブラウザで直接実行するハンズオンコードでSpring Security 6 & JWT Authenticationを演習し、24時間対応のAIチューターがレッスンを進める中での質問に答えます。
Spring Security 6 & JWT Authenticationを始めるのに経験は必要ですか？
事前経験は必要ありません。CoddyKitのSpring Security 6 & JWT Authenticationは初級者から上級者向けに構成されているため、ここから始めるか最初から始めて、自分のペースで進むことができます。 これはレッスン2/4です。
「カスタムJWTフィルターの実装」レッスンにはどのくらい時間がかかりますか？
ほとんどのCoddyKitレッスンは約5～10分かかります。各レッスンはコンパクトでインタラクティブなので、着実に進歩し、ウェブとアプリ全体で正確に前回の場所から再開できます。
このSpring Security 6 & JWT Authenticationレッスンでコードを書いて実行できますか？
はい。すべてのSpring Security 6 & JWT Authenticationレッスンに組み込みコードエディタが含まれているため、ブラウザでリアルコードを書いて実行し、即座のAIフィードバックを取得できます。ローカル設定は不要です。