asp.net web api & application/x-www-form-urlencoded

request：

POST /api/login/login HTTP/1.1
Host: localhost:8998
Connection: keep-alive
Content-Length: 27
Accept: application/json, text/javascript, */*; q=0.01
Origin: http://localhost:8998
X-Requested-With: XMLHttpRequest
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/67.0.3396.99 Safari/537.36
Content-Type: application/x-www-form-urlencoded
Referer: http://localhost:8998/HtmlPage1.html
Accept-Encoding: gzip, deflate, br
Accept-Language: zh-CN,zh;q=0.9

username=roger&password=123

server code:

    [RoutePrefix("api/login")]
    public class LoginController : ApiController
    {
        public static Dictionary<string, string> Users = new Dictionary<string, string> { { "roger", "123" }, { "apple", "321" } };

        [AcceptVerbs("POST")]
        [Route("login")]
        public string Login(User user)
        {
            var o = this;
            if (Users.ContainsKey(user.UserName))
            {
                if (user.Password == Users[user.UserName])
                {
                    return user.ToString();
                }
            }

            return "invalid username or password";
        }
    }

    public class User
    {
        public string UserName{ get; set; }
        public string Password{ get; set; }

        public override string ToString()
        {
            return UserName + "@" + Password;
        }
    }

注意事项：

正确的User类：

    public class User
    {
        public string UserName{ get; set; }
        public string Password{ get; set; }
    }

错误的User类：

    public class User
    {
        public string UserName; 
        public string Password;
    }

1. User类必须使用property，不可以使用field，后者导致不能正确反序列化，Login函数接收不到正确的参数
2. application/json无此事项
3. 公共成员变量使用property包装，不要偷懒