google oauth problem

gistfile1.txt

Following steps at https://developers.google.com/accounts/docs/OAuth2WebServer

Step 1.  submit a get request to the google api endpoint, below is example of my (seemingly) correctly formed get request

https://accounts.google.com/o/oauth2/auth?response_type=code&scope=https://mail.google.com/+https://www.googleapis.com/auth/userinfo.email+https://www.googleapis.com/auth/userinfo.profile&client_id=XXXXXXXXXXXX.apps.googleusercontent.com&redirect_uri=http://localhost:4567/oauth2callback&access_type=online

Step 2.  receive a callback that contains an authorization code, below is the url I'm receiving back. 

http://localhost:9393/oauth2callback?code=XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX.YYYYYYYYYYYYYYYYYYYYYYYYYYYYYYY

Step 3.  submit a post request to 

POST /o/oauth2/token HTTP/1.1
Host: accounts.google.com

my (seemingly) correctly formed post url

https://accounts.google.com/o/oauth2/token?code=XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX&client_id=AAAAAAAAAAAA.apps.googleusercontent.com&client_secret=ZZZZZZZZZZZZZZZZZZZZZZZZ&redirect_uri=http://localhost:4567/oauth2callback&grant_type=authorization_code 

the post url is returning json data

{
  "error" : "invalid_request"
}

so I could infer that something is incorrect in my post url.   i've tried the post url using the complete code returned in step 2 and also the xxxx portion of the token, which is the format that the google documentation uses.