Firstly, Any application that calls Google APIs needs to enable those APIs in the API Console.
Now, Any application that uses OAuth 2.0 to access Google APIs must have authorization credentials that identify the application to Google's OAuth 2.0 server.
For the credentials go to the Credentials Page and then fill the form according to your Application.
Note: Google recommends that you design your app's auth endpoints so that your application does not expose authorization codes to other resources on the page.
After getting your credentials, download the client_secret.json file from the API Console and securely store the file in a location that only your application can access.
For HTTP/REST, there is no need to install any libraries to call oAuth 2.0
Google's OAuth 2.0 endpoint is at https://accounts.google.com/o/oauth2/v2/auth. This endpoint is accessible only over HTTPS. Plain HTTP connections are refused.
As a client, the only thing you need to do for Basic authentication is to include an Authorization header in an HTTP request, composed of the username and password, separated by a colon and then Base64 encoded. E.g., in Ruby (1.9) using RestClient:
require 'restclient'
require 'base64'
auth = "Basic " + Base64::strict_encode64("#{username}:#{password}")
response = RestClient.get("https://myhost/resource",:authorization=>auth)
The token value is opaque to a client, but can be decoded by a Resource Server so it can check that the Client and User have permission to access the requested resource.
Authorization: Bearer <TOKEN_VALUE>
Send user to Google's OAuth 2.0 server. Example URL:
https://accounts.google.com/o/oauth2/v2/auth?
scope=https%3A%2F%2Fwww.googleapis.com%2Fauth%2Fdrive.metadata.readonly&
access_type=offline&
include_granted_scopes=true&
state=state_parameter_passthrough_value&
redirect_uri=http%3A%2F%2Foauth2.example.com%2Fcallback&
response_type=code&
client_id=client_id
Request access token. Example:
POST /oauth2/v4/token HTTP/1.1
Host: www.googleapis.com
Content-Type: application/x-www-form-urlencoded
code=4/P7q7W91a-oMsCeLvIaQm6bTrgtp7&
client_id=your_client_id&
client_secret=your_client_secret&
redirect_uri=https://oauth2.example.com/code&
grant_type=authorization_code
Use API. Example:
GET /drive/v2/files HTTP/1.1
Authorization: Bearer <access_token>
Host: www.googleapis.com/
