Please Add "Sign in with Google" account option#3

If I want to buy an ebook from Gumroad I can’t “Sign in Gumroad with my Google Account” but there are still options to sign in with a Twitter or Facebook account. If I want to read my bought ebook from my android device I have to put my email and password again.
Please tell your developers to implement friction less log in options both in web and mobile with the Sign in with Google account option