asp.net core api 跨域配置

项目前后端分离，前端请求接口例如使用axios发送请求时浏览器会提示跨域错误，需要后端配置允许接口跨域

配置步骤：

1、通过NuGet安装Microsoft.AspNetCore.Cors.dll类库

2、在Startup.cs中的ConfigureServices方法加入以下配置

            services.AddCors(options =>
            {
                options.AddPolicy("CorsPolicy", builder =>
                {
                    //builder.AllowAnyOrigin(); //客户端不携带cookie时，可以配置
                    builder.WithOrigins(ConfigHelper.GetSectionModel<List<string>>("CorsOrigins").ToArray()); //客户端携带cookie、或者在请求报文定义其他字段属性时，必须指定域名
                    builder.AllowAnyHeader();
                    builder.AllowAnyMethod();
                    builder.AllowCredentials();
                    builder.SetPreflightMaxAge(TimeSpan.FromSeconds());  //如果接口已验证过一次跨域，则在60分钟内再次请求时，将不需要验证跨域
                });

            });

3、在Startup.cs中的Configure方法加入以下配置

 app.UseCors("CorsPolicy");

注意：必须要加在app.UseMvc();前面

4、在appsettings.json配置可以跨域的域名：

"CorsOrigins": [ "http://www.testseparateapi.com:8080", "http://localhost:8080" ]

ConfigHelper读取appsettings.json工具类代码：

     /// <summary>
     /// appsettings.json配置文件帮助类
     /// </summary>
     public class ConfigHelper
     {
         static ConfigHelper()
         {
             Microsoft.Extensions.Configuration.IConfiguration config = AutofacHelper.GetService<Microsoft.Extensions.Configuration.IConfiguration>();
             if (config == null)
             {
                 var builder = new Microsoft.Extensions.Configuration.ConfigurationBuilder().SetBasePath(AppContext.BaseDirectory).AddJsonFile("appsettings.json");

                 config = builder.Build();
             }

             _config = config;
         }

         private static Microsoft.Extensions.Configuration.IConfiguration _config { get; }

         #region 从appsettings.json获取key的值
         /// <summary>
         /// 从appsettings.json获取key的值
         ///
         /// 列如：appsettings.json的格式如下
         ///
         /// {
         ///
         ///  "Logging": {
         ///    "LogLevel": {
         ///      "Default": "Warning"
         ///    }
         ///},
         ///  "AllowedHosts": "*",
         ///  "RabbitMQ": {
         ///    "HostName": "111",
         ///    "UserName": "11",
         ///    "Password": "11",
         ///    "ReTryCount": "5"
         ///  }
         ///}
         ///
         /// 取RabbitMQ下的HostName的值，则参数key为 RabbitMQ:HostName
         ///
         /// </summary>
         /// <param name="key">key</param>
         /// <returns></returns>
         public static string GetValue(string key)
         {
             var rr = _config.GetSection(key).GetChildren();

             return _config[key];
         }
         #endregion

         #region appsettings.json 子节点转实体
         /// <summary>
         /// appsettings.json 子节点转实体
         /// </summary>
         /// <typeparam name="T"></typeparam>
         /// <param name="key">节点名称</param>
         /// <returns></returns>
         public static T GetSectionModel<T>(string key) where T : new()
         {
             var model = new T();
             _config.GetSection(key).Bind(model);
             return model;
         }

         #endregion

         /// <summary>
         /// 获取连接字符串
         /// </summary>
         /// <param name="nameOfCon">连接字符串名</param>
         /// <returns></returns>
         public static string GetConnectionString(string nameOfCon)
         {
             return _config.GetConnectionString(nameOfCon);
         }
     }

配置允许所有域名通过跨域，builder.AllowAnyOrigin()，客户端请求的时候携带cookie或者其他参数的时候出现以下错误，必须通过builder.WithOrigins()指定域名