% go run main.go
2019/05/15 09:39:16 Open http://localhost:58806
2019/05/15 09:39:26 Got a token: &{AccessToken:... TokenType:Bearer RefreshToken:... scope:https://www.googleapis.com/auth/userinfo.email openid token_type:Bearer]}
2019/05/15 09:39:26 Your token is valid until 2019-05-15 10:39:26.720292 +0900 JST m=+3609.800317611
It will automatically open the browser and you can log in to Google.