How to Diagnose Lost Login After OAuth Return
When IdP auth succeeds but the callback page is logged out, SameSite and cookie-attribute mismatches are common root causes. Validate cookie delivery conditions before token logic.
Symptom definition
- Session disappears when returning to the OAuth/OIDC callback URL
- Same-site navigation works, but external return flow fails
- Repro rate changes by browser or environment (prod/staging)
Diagnostic steps (recommended order)
- 1) Use Set-Cookie Inspect to compare attributes before/after callback (SameSite/Secure/Path/Domain)
- 2) Reproduce send behavior with SameSite Cookie Simulator using top-level URL and request URL
- 3) Validate callback URL matching rules with Cookie Domain/Path Matcher
- 4) Detect same-name cookie conflicts (legacy Path/Domain leftovers) with Set-Cookie Conflict Checker
- 5) Audit policy requirements such as SameSite=None + Secure with Cookie Security Audit
Common root-cause patterns
- SameSite=Lax/Strict blocks cookie on cross-site callback
- SameSite=None is set without Secure and is rejected by browser policy
- Cookie Path does not cover the callback path
- Old and new same-name cookies conflict, sending unexpected values
- Host/origin differences (www/subdomain) break host-only cookie matches
Fix strategy (operations)
- For IdP return flows, design with SameSite=None; Secure as baseline
- Unify Path/Domain to the minimal callback-inclusive scope and explicitly clear legacy cookies
- If same-name use is unavoidable, separate responsibility with explicit prefixes (for example sid_app/sid_admin)
- Run regression tests with production-like HTTPS and real domains to capture browser differences
Tools for this diagnosis
- Set-Cookie Inspect
- SameSite Cookie Simulator
- Cookie Domain/Path Matcher
- Set-Cookie Conflict Checker
- Cookie Security Audit
- Host/Authority/Origin Inspect
- Set-Cookie Not Persisted Diagnostic
FAQ
- Why does it work locally but fail in production?
- Production introduces HTTPS, real domains, CDN, and IdP domain differences, which often reveals SameSite and host-only matching problems.
- What if it still fails with SameSite=None?
- Check in order: missing Secure, Path/Domain mismatch, same-name conflicts, and browser tracking-prevention restrictions.
Referenced specs
Next to view (diagnostic order)
These links are generated from site_map rules in recommended diagnostic order.
- Set-Cookie Inspect — Parse Set-Cookie attributes and review delivery policy
- SameSite Cookie Simulator — Simulate cookie send behavior from SameSite and request context
- Cookie Domain/Path Matcher — Evaluate cookie send conditions by Domain/Path/Secure
- Set-Cookie Conflict Checker — Detect same-name cookie conflicts and overwrite risks
- Cookie Security Audit — Audit Secure/HttpOnly/SameSite settings
- Host/Authority/Origin Inspect — Cross-check Host/:authority/Origin/Referer for mismatches
- How to Diagnose Set-Cookie Not Persisting — Isolate cookie persistence failures by checking Domain/Path/Secure/SameSite in order
- Cookie Incident Operational Checklist — Standardize response from triage to permanent fixes across storage failures, OAuth return issues, and same-name collisions
Same-theme links
Scenario Clusters
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- How to Diagnose Same-Name Cookie Collisions — Resolve unstable behavior by tracing same-name cookie path/domain variants, overwrite order, and send collisions
- Cookie Incident Operational Checklist — Standardize response from triage to permanent fixes across storage failures, OAuth return issues, and same-name collisions