Integration with Auth

> _This issue was auto-created as part of the Zenhub sub-issues migration. The original entity was opened on 2024-02-22. For more details see [this post](https://changelog.zenhub.com/migration-of-epics-projects-to-sub-issues-313645?zenhub_entity_id=Z2lkOi8vcmFwdG9yL1plbmh1YkVwaWMvMjA4NjU2)._

Companies and company representatives must log on to the Service BC Connect authentication in order to access the Business Transparency Register. Integration with auth in order to identify who is logged on is required.

Rules
-If you are not logged in the attempt to file a SI filing will error
-No handling in the UI currently exists (although people should not be getting into the UI without being logged in)
-If you are logged in and the user/account has access to a business then you should be able to view a dashboard and access filings, otherwise you should be halted (API: auth validation #19212). Note, may need to consider what would happen if this failed or where the API validation would kick in. If this kicks in upon submit depending on how much information is prepopulated in a change filing we may be risking exposing data.

Start with API auth validation issue #19212 and trace the existing dashboard, filing, and Service BC Connect authentication flows. Confirm where authentication and business-access checks occur, including the unauthenticated filing and failed-validation cases. Done means authorized users can access the dashboard and filings while unauthorized or unauthenticated attempts are halted without exposing filing data.

Written by the indexing model from the issue text.