Breaking changes from oauth2 v2

[espen]

Fixes #7

[espen]

There seems to be no way to tell omniauth-oauth2 that there is no refresh_token. There might be a better way than setting expires_at like this though.

[ur5us]

@espen Thanks for sharing your solution. It works for me, though I use a 1 year expiry which is plenty in my case. In general, using .year.from_now won’t work for this library though I’d presume as it relies on ActiveSupport extensions to Integer. Other than that I’m not sure either whether there’s a better way. Looking at the Ruby example for Mailchimp’s OAuth2 flow (https://mailchimp.com/developer/marketing/guides/access-user-data-oauth-2/) they do not provide an expiry param but it’s hard to tell whether they’re simply not adhering to the spec or whether it’s an issue with omniauth, oauth2, omniauth-oauth2 or this gem here.