Preserve pending OIDC interaction during signup - #562

Preserve an existing, unfinished OIDC interaction when a user navigates from login to signup. This allows registration to complete the authorization flow initiated by the application.

Standalone signup continues to create an internal interaction when no interaction exists.

Description

Problem

When a user starts login from an OIDC client application and selects Sign Up on VoidAuth, RegistrationComponent.ngOnInit() checks /api/interaction/exists.
A response of 200 with successRedirect: null means an interaction exists but authentication has not completed. Previously, the registration page discarded that interaction by calling createInteraction(true).
This starts a new authorization request for auth_internal_client, replacing the original application's authorization context. After registration, the browser follows VoidAuth's internal callback to DEFAULT_REDIRECT or APP_URL instead of returning to the application.
This causes end-user to instead of being redirected to the application's page after signing up to the VoidAuth's page. This behavior does not persist on user that are already logged in/started signing in.

Changes

Remove the branch that creates a replacement interaction when an existing interaction has not yet completed.

This matches the login page's handling:

• Preserve pending interactions.
• Follow the success redirect for completed interactions.
• Create an internal interaction when no interaction is available.

Steps to reproduce:

• Sign out of VoidAuth.
• Start login from an application configured as an OIDC client.
• Select Sign Up on VoidAuth's login page.
• Register a new account and complete or skip passkey enrollment.

Before: Registration returns to VoidAuth's default destination.

Expected: Registration resumes the original application's authorization flow, including any applicable consent or other required steps.

Validation

• Reproduced the original issue against a live deployment.
• A regression check executing the registration initializer failed before the change and passed afterward.
• Checked pending, missing, and completed interaction handling.
• Production frontend build and TypeScript check passed.
• Commit hooks passed.
• Local browser QA with mocked SSO responses confirmed signup makes no replacement internal-client authorization request and follows the supplied continuation URL.

Related Tickets & Documents

None was related as far as I know prior to the date of opening this PR.

AI Usage

AI assistance: OpenCode (Hephaestus) identified the faulty branch, removed it, and ran regression checks and browser QA.

Screenshots

None.