Web API 跨域问题

解决办法：

1、web.config

<system.webServer>
    <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>
    <httpProtocol>
      <customHeaders>
        <!--<add name="Access-Control-Allow-Origin" value="http://xxx.com, http://yyy.com" />-->
        <add name="Access-Control-Allow-Origin" value="*" />
        <add name="Access-Control-Allow-Methods" value="GET, POST, PUT, DELETE" />
      </customHeaders>
    </httpProtocol>
  </system.webServer>

<add name="Access-Control-Allow-Origin" value="*" />
<add name="Access-Control-Allow-Methods" value="GET, POST, PUT, DELETE" />
指定网站

<add name="Access-Control-Allow-Origin" value="http://xxx.com, http://yyy.com" />

2、System.Web.Http.Cors 

3、扩展