This is the first step you need to do for using any Google API request. Google API requests can be send using an ‘access token’ which can be created from a ‘refresh token’. But in order to create the refresh token, you need to allow the API permissions you want to use for the Google account through a web page. This will give you an access code which is required for creating a refresh token. This permission approval and code generation is required every time you need to create a new refresh token.
Replace the required values in the following URL and open the URL in a browser window where you are Google account is logged in.
https://accounts.google.com/o/oauth2/v2/auth?scope={required scope}&access_type=offline&include_granted_types=true&response_type=code&state=state_parameter_passthrough_value&redirect_uri=http://localhost&client_id={client ID}
e.g.
https://accounts.google.com/o/oauth2/v2/auth?scope=https://www.googleapis.com/auth/drive.file&access_type=offline&include_granted_types=true&response_type=code&state=state_parameter_passthrough_value&redirect_uri=http://localhost&client_id=################.apps.googleusercontent.com