Eliminate code duplication in OIDC identity creation (#230)

* Eliminate duplication by using create_from_omniauth method

- Updated OidcIdentity.create_from_omniauth to set last_authenticated_at
- Refactored OidcAccountsController to use create_from_omniauth instead of direct create! calls
- Updated test to verify last_authenticated_at is set by create_from_omniauth

Co-authored-by: jjmata <187772+jjmata@users.noreply.github.com>

* Extract auth hash building into private helper method

- Added build_auth_hash helper method to eliminate OpenStruct creation duplication
- Both create_link and create_user actions now use the same helper

Co-authored-by: jjmata <187772+jjmata@users.noreply.github.com>

* Linter fix

* Fix button style on OIDC link step

* Fix dark mode styles

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: jjmata <187772+jjmata@users.noreply.github.com>
Co-authored-by: Juan José Mata <juanjo.mata@gmail.com>

app/controllers/oidc_accounts_controller.rb

@@ -28,16 +28,9 @@ class OidcAccountsController < ApplicationController
 
     if user
       # Create the OIDC identity link
-      oidc_identity = user.oidc_identities.create!(
-        provider: @pending_auth["provider"],
-        uid: @pending_auth["uid"],
-        info: {
-          email: @pending_auth["email"],
-          name: @pending_auth["name"],
-          first_name: @pending_auth["first_name"],
-          last_name: @pending_auth["last_name"]
-        },
-        last_authenticated_at: Time.current
+      oidc_identity = OidcIdentity.create_from_omniauth(
+        build_auth_hash(@pending_auth),
+        user
       )
 
       # Clear pending auth from session
@@ -100,16 +93,9 @@ class OidcAccountsController < ApplicationController
 
     if @user.save
       # Create the OIDC identity
-      @user.oidc_identities.create!(
-        provider: @pending_auth["provider"],
-        uid: @pending_auth["uid"],
-        info: {
-          email: @pending_auth["email"],
-          name: @pending_auth["name"],
-          first_name: @pending_auth["first_name"],
-          last_name: @pending_auth["last_name"]
-        },
-        last_authenticated_at: Time.current
+      OidcIdentity.create_from_omniauth(
+        build_auth_hash(@pending_auth),
+        @user
       )
 
       # Clear pending auth from session
@@ -122,4 +108,15 @@ class OidcAccountsController < ApplicationController
       render :new_user, status: :unprocessable_entity
     end
   end
+
+  private
+
+    # Convert pending auth hash to OmniAuth-like structure
+    def build_auth_hash(pending_auth)
+      OpenStruct.new(
+        provider: pending_auth["provider"],
+        uid: pending_auth["uid"],
+        info: OpenStruct.new(pending_auth.slice("email", "name", "first_name", "last_name"))
+      )
+    end
 end