Derive every mounted path from ActiveAdmin's namespace

[senid231]

The gem hardcoded /admin for the post-sign-in landing page, the SSO login/logout routes and the OmniAuth prefix. A host that renames the namespace (config.default_namespace = :backoffice) has no /admin anywhere, so each of those either 404'd or raised. Derive them from ActiveAdmin.application.default_namespace instead, and resolve the post-sign-in path through ActiveAdmin's own root helper on whichever route set holds the host's Devise mapping.

Engine-mounted hosts need one more distinction. Devise reuses a single setting, Devise.omniauth_path_prefix, both to declare its OmniAuth routes and to tell the middleware where to listen; for an engine mounted at a prefix those are different strings, so one value put the callback route at /admin/admin/auth/oidc/callback while the middleware redirected to /admin/auth/oidc/callback. Drive them separately: path_prefix: goes to the strategy directly (honoured over OmniAuth.config.path_prefix, which Devise owns), and omniauth_route_prefix -- defaulting to omniauth_path_prefix, so main-app hosts see no change -- feeds Devise's global. Registering the strategy after the host's config/initializers makes the namespace readable there, so no after_initialize hook or Rails 8 lazy-route workaround is needed.

Covered by unit specs for the namespace derivation and a full OmniAuth round trip against spec/dummy_isolated.

[Copilot]

Pull request overview

This PR removes hardcoded /admin assumptions by deriving login/logout/OmniAuth paths (and the post-sign-in landing path) from ActiveAdmin’s configured namespace, with special handling for engine-mounted hosts where Devise’s OmniAuth route prefix and the middleware listening prefix must differ.

Changes:

• Derive login_path, logout_path, and OmniAuth prefixes from ActiveAdmin.application.default_namespace, while preserving explicit overrides.
• Split OmniAuth configuration into a per-strategy middleware path_prefix: and a Devise route declaration prefix (omniauth_route_prefix) to support mounted engines correctly.
• Add/adjust request + isolated-engine specs and update docs/templates to use ActiveAdmin::Oidc.config.omniauth_path_prefix as the source of truth for browser-visible OmniAuth request paths.

Reviewed changes

Copilot reviewed 15 out of 16 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
spec/unit/configuration_spec.rb	Adds unit coverage for namespace-derived paths and fallback behavior.
spec/requests/login_path_helper_spec.rb	Updates regression spec to assert login view uses configured OmniAuth prefix (not hardcoded).
spec/requests/disabled_user_persistence_spec.rb	Switches callback posting to configured OmniAuth prefix.
spec/requests/after_sign_in_path_spec.rb	Adds specs for post-sign-in landing path resolution via ActiveAdmin root helper.
spec/isolated/requests/isolated_engine_callback_spec.rb	Adds full round-trip coverage for isolated engine mounts with split prefixes.
spec/dummy_isolated/config/initializers/activeadmin_oidc.rb	Configures isolated dummy to override omniauth_route_prefix engine-relatively.
README.md	Documents namespace derivation and the new omniauth_route_prefix behavior for engines.
Rakefile	Minor task definition syntax update for spec:all.
lib/generators/active_admin/oidc/install/templates/sessions_new.html.erb	Uses gem config for OmniAuth request path in generated view.
lib/generators/active_admin/oidc/install/templates/sessions_new_v4.html.erb	Uses gem config for OmniAuth request path in generated v4 view.
lib/activeadmin/oidc/engine.rb	Registers strategy using per-strategy path_prefix: and sets Devise route prefix from config.
lib/activeadmin/oidc/configuration.rb	Introduces derived path helpers + omniauth_route_prefix with fallback namespace behavior.
app/views/active_admin/devise/sessions/new.html.erb	Uses gem config for OmniAuth request path instead of OmniAuth global.
app/controllers/active_admin/oidc/devise/omniauth_callbacks_controller.rb	Redirects post-sign-in via ActiveAdmin’s root helper; adds route-set dispatch helper.
.rspec	Updates guidance comment about running spec suites.
.gitignore	Adds ignore entries and db.yml exception for new dummy app paths.

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