Access-Control-Allow-Origin' header is present on the requested resource 处理办法ASP.NET

一、报错信息：Access to XMLHttpRequest at 'https://localhost:44391/api/Hold/GetLotInfoList' from origin 'http://localhost:8080' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource.

二、错误原因：在跨域访问web api的api时，C#自带的web api并不能支持跨域访问，如果需要，可以更改配置来实现


三、解决办法：
（1）允许所有来源，HTTP方法，请求标头跨域：后端，在Web.config中找到<system.webServer>标签，里面添加配置如下：
<httpProtocol>
　　<customHeaders>
　　　　<add name="Access-Control-Allow-Origin" value="*"/>
　　　　<add name="Access-Control-Allow-Headers" value="*" />
　　　　<!--<add name="Access-Control-Allow-Headers" value="Content-Type,Token" />-->
　　　　<add name="Access-Control-Allow-Methods" value="GET, POST, PUT, DELETE, OPTIONS" />
　　</customHeaders>
</httpProtocol>

具体位置如下截图：


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