Ingress 兼容前端https & http 跨域配置access-control-allow-origin

场景说明：

前端域名a访问后端b域名，其中b使用Ingress配置，需要支持http://a和https://a两种前端域名跨域方式访问b。

一、使用Ingress原生跨域Annotations配置只可满足其中一种情况

注意，官方最新的文档cors-allow-origin支持配置多个域名，但在我们使用的比较旧的版本0.32中配置两个直接被设置为*，导致失败

annotations:
  nginx.ingress.kubernetes.io/enable-cors: 'true'
  nginx.ingress.kubernetes.io/cors-allow-origin: 'https://a'
  # 或者 nginx.ingress.kubernetes.io/cors-allow-origin: 'http://a'
  nginx.ingress.kubernetes.io/cors-allow-methods: '*'
  nginx.ingress.kubernetes.io/cors-allow-headers: '*'
  nginx.ingress.kubernetes.io/cors-allow-credentials: 'true'

二、以上配置生成的nginx.conf片段

# Cors Preflight methods needs additional options and different Return Code
 if ($request_method = 'OPTIONS') {
         more_set_headers 'Access-Control-Allow-Origin: *';
         more_set_headers 'Access-Control-Allow-Credentials: true';
         more_set_headers 'Access-Control-Allow-Methods: *';
         more_set_headers 'Access-Control-Allow-Headers: *';
         more_set_headers 'Access-Control-Max-Age: 1728000';
         more_set_headers 'Content-Type: text/plain charset=UTF-8';
         more_set_headers 'Content-Length: 0';
         return 204;
 }

 more_set_headers 'Access-Control-Allow-Origin: *';
 more_set_headers 'Access-Control-Allow-Credentials: true';
 more_set_headers 'Access-Control-Allow-Methods: *';
 more_set_headers 'Access-Control-Allow-Headers: *';

三、根据自动生成的nginx.conf改为使用configuration-snippet配置

annotations:
    nginx.ingress.kubernetes.io/configuration-snippet: |
      if ($request_method = 'OPTIONS') { 
        more_set_headers "Access-Control-Allow-Origin: $http_origin"; 
        more_set_headers 'Access-Control-Allow-Credentials: true'; 
        more_set_headers 'Access-Control-Allow-Methods: *';
        more_set_headers 'Access-Control-Allow-Headers: *';
        more_set_headers 'Access-Control-Max-Age: 1728000';
        more_set_headers 'Content-Type: text/plain charset=UTF-8';
        more_set_headers 'Content-Length: 0'; 
        return 204; 
      }   
      more_set_headers "Access-Control-Allow-Origin: $http_origin"; 
      more_set_headers 'Access-Control-Allow-Credentials: true'; 
      more_set_headers 'Access-Control-Allow-Methods: *'; 
      more_set_headers 'Access-Control-Allow-Headers: *';
    nginx.ingress.kubernetes.io/ssl-redirect: 'false'