Allow passing full_host in options

[delongtj]

Not sure if this will apply to anyone else, but since our application identifies the account using a subdomain, Mailchimp's upcoming changes to require a fully-qualified callback URL for OAuth required changes on our end.

Since each user's subdomain will be unique, we had to set up a reserved subdomain to route all these requests through rather than relying on the default behavior which will pass https://<account_subdomain>.kindful.com as part of the callback URL and lead to a mismatch.

We'll run on this fork for now, but this allows us to pass in our reserved subdomain as the full_host, which did not seem possible before.

[espen]

Are you referring to this change? https://mailchimp.com/developer/release-notes/stricter-rules-for-url-matching-oauth-2/

[espen]

I see this code is also discussed and used in other omniauth gems so it should be fine to merge.

omniauth/omniauth-oauth2#93

WebTheoryLLC/omniauth-twitch@3032f76

Personally I found that supporting custom subdomains is problematic when making generic oauth strategies as some providers only allow one URL so we route all callbacks through a specific app domain.

[delongtj]

Yes, that is the change I'm referencing.

We will be doing what you mention in your last comment and routing all OAuth requests through a specific subdomain. Even if Mailchimp allowed multiple URLs, we wouldn't want to add one for each account we have (thousands at this point).

I wavered on whether to pass in the full callback_url or only the full_host, and it seemed a little cleaner to pass the host and allow the rest of the path to use the existing methods. For our use-case, our app will use configuration to pass in the full_host option since we will have different values for local, qa, and production servers.

[stevenkaras]

Finally had a chance to go over this. Looks good. I'll push out a new version tonight.

[delongtj]

@stevenkaras thanks for accepting. It will help us a lot, and I'm thinking at least a few others who use the gem on apps with multiple subdomains 👍