<dependency>
 <groupId>org.springframework.boot</groupId>
 <artifactId>spring-boot-starter-webflux</artifactId>
</dependency>
<dependency>
 <groupId>org.springframework.boot</groupId>
 <artifactId>spring-boot-starter-security</artifactId>
</dependency>
<dependency>
 <groupId>io.jsonwebtoken</groupId>
 <artifactId>jjwt</artifactId>
 <version>0.9.1</version>
</dependency>

@Component
public class JwtTokenProvider {

  private static final String AUTHORITIES_KEY = "roles";

  private final JwtProperties jwtProperties;

  private String secretKey;

  public JwtTokenProvider(JwtProperties jwtProperties) {
    this.jwtProperties = jwtProperties;
  }

  @PostConstruct
  public void init() {
    secretKey = Base64.getEncoder().encodeToString(jwtProperties.getSecretKey().getBytes());
  }

  public String createToken(Authentication authentication) {

    String username = authentication.getName();
    Collection<? extends GrantedAuthority> authorities = authentication.getAuthorities();
    Claims claims = Jwts.claims().setSubject(username);
    if (!authorities.isEmpty()) {
      claims.put(AUTHORITIES_KEY, authorities.stream().map(GrantedAuthority::getAuthority).collect(joining(",")));
    }

    Date now = new Date();
    Date validity = new Date(now.getTime() + this.jwtProperties.getValidityInMs());

    return Jwts.builder()
        .setClaims(claims)
        .setIssuedAt(now)
        .setExpiration(validity)
        .signWith(SignatureAlgorithm.HS256, this.secretKey)
        .compact();

  }

  public Authentication getAuthentication(String token) {
    Claims claims = Jwts.parser().setSigningKey(this.secretKey).parseClaimsJws(token).getBody();

    Object authoritiesClaim = claims.get(AUTHORITIES_KEY);

    Collection<? extends GrantedAuthority> authorities = authoritiesClaim == null ? AuthorityUtils.NO_AUTHORITIES
        : AuthorityUtils.commaSeparatedStringToAuthorityList(authoritiesClaim.toString());

    User principal = new User(claims.getSubject(), "", authorities);

    return new UsernamePasswordAuthenticationToken(principal, token, authorities);
  }

  public boolean validateToken(String token) {
    try {
      Jws<Claims> claims = Jwts.parser().setSigningKey(secretKey).parseClaimsJws(token);

      if (claims.getBody().getExpiration().before(new Date())) {
        return false;
      }

      return true;
    } catch (JwtException | IllegalArgumentException e) {
      throw new InvalidJwtAuthenticationException("Expired or invalid JWT token");
    }
  }

}

public class JwtTokenAuthenticationFilter implements WebFilter {

  public static final String HEADER_PREFIX = "Bearer ";

  private final JwtTokenProvider tokenProvider;

  public JwtTokenAuthenticationFilter(JwtTokenProvider tokenProvider) {
    this.tokenProvider = tokenProvider;
  }

  @Override
  public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) {
    String token = resolveToken(exchange.getRequest());
    if (StringUtils.hasText(token) && this.tokenProvider.validateToken(token)) {
      Authentication authentication = this.tokenProvider.getAuthentication(token);
      return chain.filter(exchange)
          .subscriberContext(ReactiveSecurityContextHolder.withAuthentication(authentication));
    }
    return chain.filter(exchange);
  }

  private String resolveToken(ServerHttpRequest request) {
    String bearerToken = request.getHeaders().getFirst(HttpHeaders.AUTHORIZATION);
    if (StringUtils.hasText(bearerToken) && bearerToken.startsWith(HEADER_PREFIX)) {
      return bearerToken.substring(7);
    }
    return null;
  }
}

@Configuration
public class SecurityConfig {

  @Bean
  SecurityWebFilterChain springWebFilterChain(ServerHttpSecurity http,
                        JwtTokenProvider tokenProvider,
                        ReactiveAuthenticationManager reactiveAuthenticationManager) {

    return http.csrf(ServerHttpSecurity.CsrfSpec::disable)
        .httpBasic(ServerHttpSecurity.HttpBasicSpec::disable)
        .authenticationManager(reactiveAuthenticationManager)
        .exceptionHandling().authenticationEntryPoint(
            (swe, e) -> {
      swe.getResponse().setStatusCode(HttpStatus.UNAUTHORIZED);
      return swe.getResponse().writeWith(Mono.just(new DefaultDataBufferFactory().wrap("UNAUTHORIZED".getBytes())));
    })
        .accessDeniedHandler((swe, e) -> {
      swe.getResponse().setStatusCode(HttpStatus.FORBIDDEN);
      return swe.getResponse().writeWith(Mono.just(new DefaultDataBufferFactory().wrap("FORBIDDEN".getBytes())));
    }).and()
        .securityContextRepository(NoOpServerSecurityContextRepository.getInstance())
        .authorizeExchange(it -> it
            .pathMatchers(HttpMethod.POST, "/auth/login").permitAll()
            .pathMatchers(HttpMethod.GET, "/admin").hasRole("ADMIN")
            .pathMatchers(HttpMethod.GET, "/user").hasRole("USER")
            .anyExchange().permitAll()
        )
        .addFilterAt(new JwtTokenAuthenticationFilter(tokenProvider), SecurityWebFiltersOrder.HTTP_BASIC)
        .build();
  }


  @Bean
  public ReactiveAuthenticationManager reactiveAuthenticationManager(CustomUserDetailsService userDetailsService,
                                    PasswordEncoder passwordEncoder) {
    UserDetailsRepositoryReactiveAuthenticationManager authenticationManager = new UserDetailsRepositoryReactiveAuthenticationManager(userDetailsService);
    authenticationManager.setPasswordEncoder(passwordEncoder);
    return authenticationManager;
  }
}

@RestController
@RequestMapping("/auth")
public class AuthController {

  @Autowired
  ReactiveAuthenticationManager authenticationManager;

  @Autowired
  JwtTokenProvider jwtTokenProvider;

  @PostMapping("/login")
  public Mono<String> login(@RequestBody AuthRequest request) {
    String username = request.getUsername();
    Mono<Authentication> authentication = authenticationManager.authenticate(new UsernamePasswordAuthenticationToken(username, request.getPassword()));

    return authentication.map(auth -> jwtTokenProvider.createToken(auth));
  }
}