解决asp.net mvc的跨域请求问题

web.config中配置如下内容：

<system.webServer>
	<httpProtocol>
		<customHeaders>
			<add name="Access-Control-Allow-Origin" value="*" />
			<add name="Access-Control-Allow-Headers" value="Content-Type" />
			<add name="Access-Control-Allow-Methods" value="GET, POST, PUT, DELETE, OPTIONS" />
		</customHeaders>
	</httpProtocol>
	<handlers>
		<remove name="ExtensionlessUrlHandler-Integrated-4.0" />
		<remove name="OPTIONSVerbHandler" />
		<remove name="TRACEVerbHandler" />
		<add name="ExtensionlessUrlHandler-Integrated-4.0" path="*." verb="*" type="System.Web.Handlers.TransferRequestHandler" preCondition="integratedMode,runtimeVersionv4.0" />
	</handlers>
</system.webServer> 

如果是webapi，还需要在每个controller中添加一个方法：

public string Options()
{
    return null;
}