This improves the error message(s) displayed when an error happens while
using a social login to log in / sign up into a Discourse community.
Unfortunately, we can't be super precise in the reason behind the error
(it can be the user clicked "cancel" during the authorization phase, or
any of the plethora of other possible errors) because the reason isn't
provided (either for security reasons, or because it's just hard to do
so in a reliable & consistent way accross all social logins).
The best I could do was to
- add the name of the "social login" provider in the error message
- tweak the copy a bit for the different cases handle
- fix the CSS/HTML to match the one used by the main application
In order to show the name of the provider, we use either the "provider"
or the "strategy" query parameter, or use the name of the authenticator
(if it's the only one enabled).
Internal ref - t/153662
---
**BEFORE**
**AFTER**
LinkedIn has grandfathered its old OAuth2 provider. This can only be used by existing apps. New apps have to use the new OIDC provider.
This PR adds a linkedin_oidc provider to core. This will exist alongside the discourse-linkedin-auth plugin, which will be kept for those still using the deprecated provider.
