Cut over website to identify to PostHog by keycloak sub instead of email

[Will-Howard]

Description

This is the final step to cut PostHog over to solely identifying users by the Keycloak sub value rather than email. There is just a auth.sub ?? auth.email left in to catch users who haven't refreshed their auth since the migration started.

Issue

#2713

Developer checklist

• Front-end code follows Component Accessibility Checklist (for Testing)
• Considered having snapshot tests and/or happy path functional tests
• Considered adding Storybook stories

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📥 Commits

Reviewing files that changed from the base of the PR and between ba44a19 and b8f58f1.

📒 Files selected for processing (4)

• apps/website/src/lib/utils.test.ts
• apps/website/src/lib/utils.ts
• libraries/ui/src/utils/auth.test.tsx
• libraries/ui/src/utils/auth.tsx

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch wh-2713-website-identify-sub

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[Will-Howard]

@coderabbitai review @greptileai review

[coderabbitai]

@Will-Howard: I’ll review the changes in #2806.

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[greptile-apps]

Greptile Summary

This PR completes the PostHog identity migration by switching from email-based identification to Keycloak sub-based identification, removing the now-redundant posthog.alias call. A sub ?? email fallback gracefully handles sessions stored before PR #2755 that have not yet been refreshed.

• auth.tsx: posthog.identify now uses auth.sub ?? auth.email as the distinct ID (email as a person property), and the posthog.alias(sub, email) call is removed since the alias was established in the prior migration step.
• utils.ts: The form-URL guard for the PostHog distinct ID is changed from !distinctId.includes('@') (an email heuristic that breaks now that subs are UUID-like) to !useAuthStore.getState().auth (a proper auth-state check), correctly suppressing the ID for any logged-in user regardless of identifier format.

Confidence Score: 5/5

Safe to merge — the changes are a straightforward final cut-over of a well-staged migration, with no breaking logic and proper fallback handling for old sessions.

Both changed behaviour paths (auth identification and form-URL distinct-ID guard) are covered by updated unit tests. The fallback for pre-migration sessions is explicit and tested. The removal of posthog.alias is intentional since the alias was established in a prior migration step, and the auth-state guard in utils.ts correctly supersedes the brittle email-heuristic it replaces.

No files require special attention.

Important Files Changed

Filename	Overview
libraries/ui/src/utils/auth.tsx	Switches PostHog identification from email to keycloak sub, removes alias call, adds email fallback for old sessions pre-#2755
apps/website/src/lib/utils.ts	Replaces the !distinctId.includes('@') email heuristic with !useAuthStore.getState().auth auth-state check for guarding distinct ID forwarding to form URLs
libraries/ui/src/utils/auth.test.tsx	Updates tests to match new identify-by-sub behavior and verifies no alias is called; adds coverage for the email fallback path
apps/website/src/lib/utils.test.ts	Replaces email-based distinct ID guard test with an auth-state-based test using try/finally cleanup; test description updated to match new semantics

Sequence Diagram

%%{init: {'theme': 'neutral'}}%%
sequenceDiagram
    participant Browser
    participant AuthStore as useAuthStore
    participant PostHog

    Note over Browser,PostHog: Login flow (after this PR)
    Browser->>AuthStore: "setAuth({ sub, email, ... })"
    AuthStore->>PostHog: "identify(sub ?? email, { email })"
    Note over PostHog: sub used as distinct_id, email as person property

    Note over Browser,PostHog: buildApplicationUrl (logged-out visitor)
    Browser->>AuthStore: getState().auth null
    Browser->>PostHog: get_distinct_id() UUID
    Browser->>Browser: "append prefill_PostHog Distinct ID=UUID"

    Note over Browser,PostHog: buildApplicationUrl (logged-in user)
    Browser->>AuthStore: getState().auth truthy
    Browser->>Browser: skip distinct ID

    Note over Browser,PostHog: Logout
    Browser->>AuthStore: setAuth(null)
    AuthStore->>PostHog: reset()

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sequenceDiagram
    participant Browser
    participant AuthStore as useAuthStore
    participant PostHog

    Note over Browser,PostHog: Login flow (after this PR)
    Browser->>AuthStore: "setAuth({ sub, email, ... })"
    AuthStore->>PostHog: "identify(sub ?? email, { email })"
    Note over PostHog: sub used as distinct_id, email as person property

    Note over Browser,PostHog: buildApplicationUrl (logged-out visitor)
    Browser->>AuthStore: getState().auth null
    Browser->>PostHog: get_distinct_id() UUID
    Browser->>Browser: "append prefill_PostHog Distinct ID=UUID"

    Note over Browser,PostHog: buildApplicationUrl (logged-in user)
    Browser->>AuthStore: getState().auth truthy
    Browser->>Browser: skip distinct ID

    Note over Browser,PostHog: Logout
    Browser->>AuthStore: setAuth(null)
    AuthStore->>PostHog: reset()

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