Set the value to offline if your application needs to refresh access tokens when the user is not present at the browser. This is the method of refreshing access tokens described later in this document. This value instructs the Google authorization server to return a refresh token and an access token the first time that your application exchanges an authorization code for tokens.
Google responds to this request by returning a JSON object that contains a short-lived access token and a refresh token. Note that the refresh token is only returned if your application set the access_type parameter to offline in the initial request to Google's authorization server.
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