beego api 服务允许跨域访问，解决前端访问报Access-Control-Allow-Origin问题

背景：

　　golang做了个简单服务，前端get请求拿数据，报错：No 'Access-Control-Allow-Origin' header is present on the requested

如何解决：

1、据说ajax可以解决（本人没试过）

2、服务端设置，允许跨域请求：在路由中添加如下设置即可

　　beego.InsertFilter("*", beego.BeforeRouter, cors.Allow(&cors.Options{
        AllowAllOrigins:  true,
        AllowMethods:     []string{"*"},
        AllowHeaders:     []string{"Origin", "Authorization", "Access-Control-Allow-Origin"},
        ExposeHeaders:    []string{"Content-Length", "Access-Control-Allow-Origin"},
        AllowCredentials: true,
    }))

特别感谢：https://studygolang.com/articles/7330

==================================2018/1/6================================================

今天再次碰到：Request header field Content-Type is not allowed by Access-Control-Allow-Headers in preflight response

没有仔细看错误信息，又卡了一个多小时。很明显是Content-Type不允许嘛，那就在 AllowHeaders把Content-Type加上就好了

哎哎-------被坑的弱智了

AllowHeaders:     []string{"Origin", "Authorization", "Access-Control-Allow-Origin", "content-type"}

================================2018/1/9==================================================

A wildcard '*' cannot be used in the 'Access-Control-Allow-Origin' header when the credentials flag is true

很明显，AllowCredentials: true的时候，返回header的Access-Control-Allow-Origin不能为*；那如何配？？？

答案：不能用AllowAllOrigins: true，必须指定可访问域名AllowOrigins

beego.InsertFilter("*", beego.BeforeRouter, cors.Allow(&cors.Options{
                //AllowAllOrigins:  true,
                AllowMethods:     []string{"*"},
                AllowHeaders:     []string{"Origin", "Authorization", "Access-Control-Allow-Origin", "content-type"},
                ExposeHeaders:    []string{"Content-Length", "Access-Control-Allow-Origin"},
                AllowCredentials: true,
                AllowOrigins: []string{"http://10.*.*.*:*","http://localhost:*","http://127.0.0.1:*"},
        }))