web api 跨域

1.首先在nuget里搜索 Microsoft.AspNet.WebApi.Cors  然后安装

2.然后在App_Start下  WebApiConfig.CS里：

var allowOrigins = ConfigurationManager.AppSettings["cors_allowOrigins"];
var allowHeaders = ConfigurationManager.AppSettings["cors_allowHeaders"];
var allowMethods = ConfigurationManager.AppSettings["cors_allowMethods"];

//跨域请求
var globalCors = new EnableCorsAttribute(allowOrigins, allowHeaders, allowMethods);
config.EnableCors(globalCors);