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src/main/java/demo/api/jwt/JwtTokenFilter.java

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+package demo.api.jwt;
+
+import demo.api.jwt.exception.CustomException;
+import java.io.IOException;
+import javax.servlet.FilterChain;
+import javax.servlet.ServletException;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+import org.springframework.security.core.Authentication;
+import org.springframework.security.core.context.SecurityContextHolder;
+import org.springframework.web.filter.OncePerRequestFilter;
+
+// Request 이전에 1회 작동할 필터
+public class JwtTokenFilter extends OncePerRequestFilter {
+  private JwtTokenProvider jwtTokenProvider;
+
+  public JwtTokenFilter(JwtTokenProvider jwtTokenProvider) {
+    this.jwtTokenProvider = jwtTokenProvider;
+  }
+
+  @Override
+  protected void doFilterInternal(
+      HttpServletRequest request,
+      HttpServletResponse response,
+      FilterChain filterChain
+  ) throws ServletException, IOException {
+    String token = jwtTokenProvider.resolveToken(request);
+    try {
+      if (token != null && jwtTokenProvider.validateToken(token)) {
+        Authentication auth = jwtTokenProvider.getAuthentication(token);
+        SecurityContextHolder.getContext().setAuthentication(auth);
+      }
+    } catch (CustomException ex) {
+      //this is very important, since it guarantees the user is not authenticated at all
+      SecurityContextHolder.clearContext();
+      response.sendError(ex.getHttpStatus().value(), ex.getMessage());
+      return;
+    }
+
+    filterChain.doFilter(request, response);
+  }
+}

src/main/java/demo/api/jwt/JwtTokenProvider.java

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+package demo.api.jwt;
+
+import demo.api.jwt.exception.CustomException;
+import io.jsonwebtoken.Claims;
+import io.jsonwebtoken.ExpiredJwtException;
+import io.jsonwebtoken.JwtException;
+import io.jsonwebtoken.Jwts;
+import io.jsonwebtoken.MalformedJwtException;
+import java.util.Base64;
+import java.util.Date;
+import javax.servlet.http.HttpServletRequest;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.http.HttpStatus;
+import org.springframework.security.core.Authentication;
+import org.springframework.security.core.userdetails.UserDetails;
+import org.springframework.security.core.userdetails.UserDetailsService;
+import org.springframework.stereotype.Component;
+import javax.annotation.PostConstruct;
+
+// 유저 정보로 JWT 토큰을 만들거나 토큰을 바탕으로 유저 정보를 가져옴
+@Component
+public class JwtTokenProvider {
+  /**
+   * THIS IS NOT A SECURE PRACTICE! For simplicity, we are storing a static key here. Ideally, in a
+   * microservices environment, this key would be kept on a config-server.
+   */
+  @Value("${jwt.token.open-secret-key}")
+  private String secret_key;
+
+  @Value("${jwt.token.expire-length}")
+  private long expire_time;
+
+  @Autowired
+  private UserDetailsService userDetailsService;
+
+  @PostConstruct // 의존성 주입이 이루어진 후 초기화를 수행
+  protected void init() {
+    secret_key = Base64.getEncoder().encodeToString(secret_key.getBytes());
+  }
+
+  public String createToken(String username, List<AppUserRole> appUserRoles) {
+
+    Claims claims = Jwts.claims().setSubject(username);
+    claims.put("auth", appUserRoles.stream().map(s -> new SimpleGrantedAuthority(s.getAuthority())).filter(Objects::nonNull).collect(Collectors.toList()));
+
+    Date now = new Date();
+    Date validity = new Date(now.getTime() + expire_time);
+
+    return Jwts.builder()
+        .setClaims(claims)
+        .setIssuedAt(now)
+        .setExpiration(validity)
+        .signWith(SignatureAlgorithm.HS256, secret_key)
+        .compact();
+  }
+
+  public Authentication getAuthentication(String token) {
+    UserDetails userDetails = userDetailsService.loadUserByUsername(getUsername(token));
+    return new UsernamePasswordAuthenticationToken(userDetails, "", userDetails.getAuthorities());
+  }
+
+  public String getUsername(String token) {
+    return Jwts.parser().setSigningKey(secret_key).parseClaimsJws(token).getBody().getSubject();
+  }
+
+  public String resolveToken(HttpServletRequest req) {
+    String bearerToken = req.getHeader("Authorization");
+    if (bearerToken != null && bearerToken.startsWith("Bearer ")) {
+      return bearerToken.substring(7);
+    }
+    return null;
+  }
+
+  public boolean validateToken(String token) {
+    try {
+      Jwts.parser().setSigningKey(secret_key).parseClaimsJws(token);
+      return true;
+    } catch (JwtException e) {
+      // MalformedJwtException | ExpiredJwtException | IllegalArgumentException
+      throw new CustomException("Error on Token", HttpStatus.INTERNAL_SERVER_ERROR);
+    }
+  }
+}

src/main/java/demo/api/jwt/exception/CustomException.java

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+package demo.api.jwt.exception;
+
+import org.springframework.http.HttpStatus;
+
+public class CustomException extends RuntimeException {
+
+  private static final long serialVersionUID = 1L;
+
+  private final String message;
+  private final HttpStatus httpStatus;
+
+  public CustomException(String message, HttpStatus httpStatus) {
+    this.message = message;
+    this.httpStatus = httpStatus;
+  }
+
+  @Override
+  public String getMessage() {
+    return message;
+  }
+
+  public HttpStatus getHttpStatus() {
+    return httpStatus;
+  }
+
+}