@Bean
public SecurityWebFilterChain springSecurityFilterChain(ServerHttpSecurity http,
    ReactiveClientRegistrationRepository clientRegistrationRepository) {
  // Authenticate through configured OpenID Provider
  http.oauth2Login();

  // Also logout at the OpenID Connect provider
  http.logout(logout -> logout.logoutSuccessHandler(
    new OidcClientInitiatedServerLogoutSuccessHandler(clientRegistrationRepository)));

  // Require authentication for all requests
  http.authorizeExchange().anyExchange().authenticated();

  // Allow showing /home within a frame
  http.headers().frameOptions().mode(Mode.SAMEORIGIN);

  // Disable CSRF in the gateway to prevent conflicts with proxied service CSRF
  http.csrf().disable();
  return http.build();
}

spring:
  security:
    oauth2:
      client:
        provider:
          keycloak:
            issuer-uri: http://localhost:8090/auth/realms/spring-cloud-gateway-realm
            user-name-attribute: preferred_username
        registration:
          keycloak:
            client-id: spring-cloud-gateway-client
            client-secret: 016c6e1c-9cbe-4ad3-aee1-01ddbb370f32

spring:
  cloud:
    gateway:
      default-filters:
      - TokenRelay
      routes:
      - id: flights-service
        uri: http://127.0.0.1:8081/flights
        predicates:
        - Path=/flights/**
      - id: hotels-service
        uri: http://127.0.0.1:8082/hotels
        predicates:
        - Path=/hotels/**

@Configuration
@EnableWebSecurity
public class SecurityConfig extends WebSecurityConfigurerAdapter {

  @Override
  protected void configure(HttpSecurity http) throws Exception {
    // Validate tokens through configured OpenID Provider
    http.oauth2ResourceServer().jwt().jwtAuthenticationConverter(jwtAuthenticationConverter());
    // Require authentication for all requests
    http.authorizeRequests().anyRequest().authenticated();
    // Allow showing pages within a frame
    http.headers().frameOptions().sameOrigin();
  }

  ...
}

private JwtAuthenticationConverter jwtAuthenticationConverter() {
  JwtAuthenticationConverter converter = new JwtAuthenticationConverter();
  // Convert realm_access.roles claims to granted authorities, for use in access decisions
  converter.setJwtGrantedAuthoritiesConverter(new KeycloakRealmRoleConverter());
  return converter;
}
[...]
class KeycloakRealmRoleConverter implements Converter<Jwt, Collection<GrantedAuthority>> {
  @Override
  public Collection<GrantedAuthority> convert(Jwt jwt) {
    final Map<String, Object> realmAccess = (Map<String, Object>) jwt.getClaims().get("realm_access");
    return ((List<String>) realmAccess.get("roles")).stream()
      .map(roleName -> "ROLE_" + roleName)
      .map(SimpleGrantedAuthority::new)
      .collect(Collectors.toList());
  }
}

@Bean
public JwtDecoder jwtDecoderByIssuerUri(<a  rel="external nofollow"  target="_blank" >OAuth2</a>ResourceServerProperties properties) {
  String issuerUri = properties.getJwt().getIssuerUri();
  NimbusJwtDecoder jwtDecoder = (NimbusJwtDecoder) JwtDecoders.fromIssuerLocation(issuerUri);
  // Use preferred_username from claims as authentication name, instead of UUID subject
  jwtDecoder.setClaimSetConverter(new UsernameSubClaimAdapter());
  return jwtDecoder;
}
[...]
class UsernameSubClaimAdapter implements Converter<Map<String, Object>, Map<String, Object>> {

  private final MappedJwtClaimSetConverter delegate = MappedJwtClaimSetConverter.withDefaults(Collections.emptyMap());

  @Override
  public Map<String, Object> convert(Map<String, Object> claims) {
    Map<String, Object> convertedClaims = this.delegate.convert(claims);
    String username = (String) convertedClaims.get("preferred_username");
    convertedClaims.put("sub", username);
    return convertedClaims;
  }

}

server:
  port: 8082
  servlet:
    context-path: /hotels/

spring:
  security:
    oauth2:
      resourceserver:
        jwt:
          issuer-uri: http://localhost:8090/auth/realms/spring-cloud-gateway-realm