Well, because it already exists? All email clients need to do: - Open a link in a browser (don't you dare open it in an embedded browser, I will find you and f

Well, because it already exists? All email clients need to do: - Open a link in a browser (don't you dare open it in an embedded browser, I will find you and force you to type 100 characters as I dictate it to you) - Handle callback. That's all. That's the entire authentication. There is probably not a single platform (language and maybe a framework) that is used to build an email client and has no library to handle this with a few lines of code. I think that's a much better and easier solution than make developers of email clients handle the very possible authentication method email providers could come up with (see reply to my comment about 2FA with Google). Also, old opera with torrent client, calendar, compressing proxy, email client was the best.