如何在c#中使用post将json值传递给API

我是c#新手，你能告诉我在c#中使用POST将json值传递给API的最佳方法吗?

下面我写了python代码，但不确定如何在c#中实现。

string payload = {
   "username" : "1432143352759a61bca0ad4a35a4f0", # when you register, they'll return this
   "password" : "password",
   "client_id" : "c3ca1565b0dbedd74c5c",
   "client_secret" : "e0591fe41c4e2585b313ad93e2748022db3186d0",
}
res = requests.post("https://sandbox.synapsepay.com/api/v2/user/login", payload)
print res.status_code
print res.text