Use Google API

To use Google API, need several steps

1. Create a developer token
2. Create a project
3. Get client id and client secret for the project
4. Get a refresh token from user by asking them to grant permission to the project (see the below)

Ask user to grant permission to get refresh token

1. Create a return url which will process code after user grant the permission
2. Add the above url to authorized redirect URIs field of the project
3. Use client library to generate an onboard url and redirect user to this url
4. After user redirect to that url, user will be asked to grant permission

With developer token, project's client id and secret, and user's refresh token, we can implement the project using Google's client library to implement the project.