When we first added OIDC support, we were configuring the redirect URI
in the devise initializer, just like we did for other providers.
Thanks to the changes in the previous commit, that code is no longer in
the devise initializer, which means we can use `url_helpers` to get the
redirect URI.
This means we no longer need to define this URI in the secrets. This is
particularly useful for multitenancy; previously, we had to define the
redirect URI for every tenant because different tenants use different
domains or different subdomains.
- name: :oidc → Identifier for this login provider in the app.
- scope: [:openid, :email, :profile] → Tells the provider we want the user’s ID (openid), their email, and basic profile info (name, picture, etc.).
- response_type: :code → Uses Authorization Code Flow, which is more secure because tokens are not exposed in the URL.
- issuer: Rails.application.secrets.oidc_issuer → The base URL of the OIDC provider (e.g., Auth0). Used to find its config.
- discovery: true → Automatically fetches the provider’s endpoints from its discovery document instead of manually setting them.
- client_auth_method: :basic → Sends client ID and secret using HTTP Basic Auth when exchanging the code for tokens.
Add system tests for OIDC Auth
Edit the oauth docs to support OIDC auth
Note that, in order to have some consistency, we're always writing
"Consul Democracy", instead of using capital letters sometimes (but not
always), like we did until now.
