Hi, Yoshihiro. Thank you very much for the article on Medium!
May I ask you for some advice?
I've downloaded the example you provided (from GitHub) and tried to run it but when I try to authorise with my Google account I get stuck in a browser window on a page google.com after I press the button "Allow". It seems that the redirect doesn't work correctly or I did something wrong.
Thank you.
I added a credential in https://console.cloud.google.com/ for the OAuth Android app type.
In the project I put secret.txt file with ClientId