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(60));  //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