Google OAuth代码不包含刷新令牌

Question

我想通过gmail发送谷歌api电话来发送邮件。

为此，我首先向oauth服务器发出以下请求：

https://accounts.google.com/o/oauth2/v2/auth?response_type=code&client_id=SOMECLIENTID&access_type=offline&redirect_uri=http://localhost:63878/Default.aspx&scope=https://www.googleapis.com/auth/gmail.send

请注意，在我的请求中，我已包含access_type = offline

它将我重定向到POST https://accounts.google.com/AccountChooser，然后我使用我的帐户登录，同意并重定向回到此页面：

HTTP/1.1 302 Moved Temporarily
Content-Type: text/html; charset=UTF-8
Cache-Control: no-cache, no-store, max-age=0, must-revalidate
Pragma: no-cache
Expires: Mon, 01 Jan 1990 00:00:00 GMT
Date: Wed, 01 Jun 2016 06:30:37 GMT
Location: http://localhost:63878/Default.aspx?code=4/LF9pQo8EH-SZkkDJV0ttNnVMIwjwWLgnc-H-QjLg__k#
Content-Language: en
Content-Encoding: gzip

在小提琴手上看到。

现在使用此代码，我再打一次电话：

POST https://www.googleapis.com/oauth2/v4/token HTTP/1.1
Host: www.googleapis.com
Connection: keep-alive
Content-Length: 266
Cache-Control: no-cache
Origin: chrome-extension://fhbjgbiflinjbdggehcddcbncdddomop
Content-Type: application/x-www-form-urlencoded
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/50.0.2661.102 Safari/537.36
Postman-Token: e9716588-2f62-d761-1c07-41c6dc057f0f
Accept: */*
X-Client-Data: CIm2yQEIorbJAQjEtskBCLKVygEI/ZXKAQjgmMoBCO2cygE=
Accept-Encoding: gzip, deflate, br
Accept-Language: en-US,en;q=0.8

code=4/LF9pQo8EH-SZkkDJV0ttNnVMIwjwWLgnc-H-QjLg__k#&client_id=SOMECLIENTID&client_secret=SOMESECRET&redirect_uri=http%3A%2F%2Flocalhost%3A63878%2FDefault.aspx&grant_type=authorization_code

我得到的回应是：

{
  "access_token":"ya29.CjLzAuW07My8BHnaMaLWjhKsD2FvzI6SpUHqdqQwkugTW4lMnQl0rXt6cQdm0ir4RObYEg",
  "token_type": "Bearer",
  "expires_in": 3557
}

为什么这不包括响应中的刷新令牌？