在Spring 5 Webflux中，配置CORS，可以通过自定义WebFilter实现：

注：此种写法需真实跨域访问，监控header中才会带相应属性。

代码实现方式

import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpStatus;
import org.springframework.http.server.reactive.ServerHttpRequest;
import org.springframework.http.server.reactive.ServerHttpResponse;
import org.springframework.web.cors.reactive.CorsUtils;
import org.springframework.web.server.ServerWebExchange;
import org.springframework.web.server.WebFilter;
import org.springframework.web.server.WebFilterChain;
import org.springframework.http.HttpMethod;
import reactor.core.publisher.Mono;

import static org.springframework.web.cors.CorsConfiguration.ALL;
public class XXXApplication{
public static void main(String[] args) {
    SpringApplication.run(XXXApplication.class, args);
}
private static final String MAX_AGE = "18000L";
@Bean
public WebFilter corsFilter() {
    return (ServerWebExchange ctx, WebFilterChain chain) -> {
        ServerHttpRequest request = ctx.getRequest();
        if (!CorsUtils.isCorsRequest(request)) {
            return chain.filter(ctx);
        }
        HttpHeaders requestHeaders = request.getHeaders();
        ServerHttpResponse response = ctx.getResponse();
        HttpMethod requestMethod = requestHeaders.getAccessControlRequestMethod();
        HttpHeaders headers = response.getHeaders();
        headers.add(HttpHeaders.ACCESS_CONTROL_ALLOW_ORIGIN, requestHeaders.getOrigin());
        headers.addAll(HttpHeaders.ACCESS_CONTROL_ALLOW_HEADERS, requestHeaders.getAccessControlRequestHeaders());
        if (requestMethod != null) {
            headers.add(HttpHeaders.ACCESS_CONTROL_ALLOW_METHODS, requestMethod.name());
        }
        headers.add(HttpHeaders.ACCESS_CONTROL_ALLOW_CREDENTIALS, "true");
        headers.add(HttpHeaders.ACCESS_CONTROL_EXPOSE_HEADERS, ALL);
        headers.add(HttpHeaders.ACCESS_CONTROL_MAX_AGE, MAX_AGE);
        if (request.getMethod() == HttpMethod.OPTIONS) {
            response.setStatusCode(HttpStatus.OK);
            return Mono.empty();
        }
        return chain.filter(ctx);
    };
}
}

配置实现方式

网上还提到一种配置写法，实测好用（感谢评论兄弟fiberhuo补充）：

spring:
  cloud:
    gateway:
      globalcors:
        corsConfigurations:
          '[/**]':
            allowedOrigins: "*"
            allowedMethods: "*"
            allowedHeaders: "*"