How to get Google OAuth 2.0 Access token directly using curl? (without using Google Libraries)

Question

I'm trying to follow this tutorial to authenticate with Google using their OAuth 2.0 API. However, I would like to make straight curl calls rather than use their libraries.

I have obtained my Client ID and Client Secret Key. Now I'm trying to get the access token like this:

curl \
--request POST \
--header "Content-Type: application/json" \
--data '{
  "client_id":"MY_CLIENT_ID",
  "client_secret":"MY_SECRET_KEY",
  "redirect_uri": "http://localhost/etc",
  "grant_type":"authorization_code"
}' \
"https://accounts.google.com/o/oauth2/token"

However, it is not working. It gives me the following error:

{
  "error" : "invalid_request",
  "error_description" : "Required parameter is missing: grant_type"
}

Can someone please provide me sample curl call to obtain the access token (and refresh token)?

Answer 1

a) the data you provide should be form-encoded instead of presented as a JSON object and b) you should also provide an authorization code value in the "code" parameter. E.g.:

curl -d "client_id=MY_CLIENT_ID&\
  client_secret=MY_SECRET_KEY&\
  redirect_uri=http://localhost/etc&\
  grant_type=authorization_code&\
  code=CODE" https://oauth2.googleapis.com/token

Answer 2

While not directly using CURL, you can also get and test OAuth tokens using the Google OAuth Playground: https://developers.google.com/oauthplayground/