Operational Runbook: Responding to a Third-Party CDN Outage That Breaks Authentication Flows

Immediate runbook: when a third‑party CDN outage breaks your authentication flows

Hook: When a CDN or security provider fails, sign‑ins fail faster than marketing pages. In 2026 incidents (most recently a January outage that affected major platforms via a Cloudflare disruption), identity workflows are often the first thing to break—and the hardest to restore without a plan. This runbook gives IT ops, DevOps and identity engineers a step‑by‑step operational playbook to triage, communicate, fail over, and run a rigorous postmortem so authentication is restored safely and fast.

Executive summary (do this first)

1. Confirm and scope the outage in 5–15 minutes.
2. Communicate to stakeholders and open an incident channel.
3. Apply safe failover: bypass the CDN or switch to backup paths that preserve TLS and session integrity.
4. Mitigate fraud and data exposure risks while restoring service.
5. Validate, reintroduce the CDN, and complete a blameless postmortem and remediation plan.

Why this matters in 2026

Third‑party vendor consolidation and multi‑layered edge services have improved performance and security—but they also create systemic single points of failure. In late 2025 and early 2026 we saw high‑visibility outages where CDN and cyber‑security provider incidents cascaded into authentication failures at scale. Identity flows (OIDC discovery, SAML metadata, cookie/session delivery, MFA challenge) are tightly coupled with edge behavior—so a broken edge can take down login and SSO faster than your homepage.

Key objectives for operations

• Restore safe access without bypassing security controls permanently.
• Minimize account takeover risk while enabling legitimate users.
• Communicate transparently to customers and regulators.
• Capture evidence for a blameless postmortem and vendor escalation.

Pre‑incident prep (what to have ready)

Start here before an outage. If you haven’t prepared these artifacts and runbooks, treat the next outage as a high‑priority remediation item.

• Dependency inventory: list all CDN, WAF, bot management and DDoS providers used for auth endpoints (include account IDs, contract contacts, and support escalation paths). See our guidance on edge auditability and decision planes for documenting provider dependencies and escalation paths.
• Service map for auth flows: document endpoints for OIDC /.well‑known/openid‑configuration, SAML metadata, token issuance, refresh token endpoints, and the MFA challenge endpoints—mark which pass through the CDN.
• Test harnesses: synthetic login checks (credentials in vault), SSO assertion tests, and API token tests that run every minute and alert on 5xx or malformed responses. Build these as part of your broader SRE and synthetic observability program.
• Failover design: primary vs backup CDN, DNS TTL strategy, direct origin access paths, and emergency TLS certs or ACM/Let’s Encrypt automation for origin certificates. For edge-host and pocket-edge patterns, see notes on pocket edge hosts and small‑footprint origin strategies.
• Runbook snippets: exact commands for dig, curl, provider console steps, Terraform or IaC snippets for DNS updates, and a checklist for rotating keys if needed. Keep these snippets near your incident artifacts and alongside a downloadable incident response template.

Incident timeline & roles

Assign roles up front. Example:

• Incident Lead (coordinates) — tie into your broader site reliability playbooks.
• Network/Edge Engineer (CDN, DNS changes)
• Identity Engineer (IDP, token, SSO flows)
• Security Lead (fraud, session integrity) — coordinate with teams responsible for password hygiene and automated rotation when credential exposure is suspected.
• Communications Lead (status updates)
• Support Liaison (CS/PS escalation)

Step‑by‑step runbook

0–5 minutes: Detect and confirm

• Check synthetic alerts and error dashboards for spikes in 5xx/502/524 on auth endpoints. Your synthetic suite should be tied into your SRE monitoring.
• Confirm user reports and support tickets affecting login, MFA, or account recovery.
• Collect quick artifacts: sample failing HTTP responses, timestamped headers, and the output of curl -v to the token endpoint and /.well‑known endpoints. Store artifacts alongside a canonical incident response checklist.
• Check vendor status pages (CDN, WAF provider) and global outage aggregators, but treat vendor pages as one signal among many. Use your edge decision plane notes to map vendor impact to service owners.

5–15 minutes: Scope and declare incident

• Is the failure localized (region, POP) or global? Use RUM, synthetic locations, and logs to scope.
• Open an incident channel (Slack/MS Teams) and create an incident ticket with initial severity. Keep updates documented in a standard incident template: incident response template.
• Set a target first update (e.g., next 15 minutes) to avoid silence and reassure customers.
• Capture the exact error strings—are you seeing certificate errors, CORS errors, or token signature validation failures? These clues indicate whether the CDN is stripping headers or altering TLS.

15–30 minutes: Quick mitigations that preserve security

Don't rush to expose origin keys or disable security controls permanently. Follow a staged approach:

1. Temporarily disable non‑critical edge features that touch auth traffic (e.g., bot mitigation or aggressive WAF rules) if logs show legitimate auth requests blocked. Use your edge policy playbook from the edge auditability guidance.
2. If CDN is corrupting responses (missing headers, truncated JSON), consider bypassing the CDN for auth endpoints only using path‑based rules or Page Rules to route /auth, /oauth, /.well‑known directly to origin.
3. Test the origin directly (via origin IP or temporary host entry) to confirm origin health: curl -v https://origin-host/auth/token. For small-origin and origin host patterns, see notes on pocket edge hosts and minimal origin exposures.
4. If bypassing the CDN, ensure TLS remains validated—use origin TLS certs and restrict access to known IPs or via VPN to avoid exposing auth APIs broadly. Consider mTLS and edge authorization patterns described in edge authorization guidance.

30–60 minutes: Controlled failover

Choose the least risky failover path that gets authentication working:

• DNS failover to backup CDN or direct origin:
  • Reduce DNS TTLs ahead of incidents as part of prep. If TTL is high, prefer HTTP path rules rather than full DNS swaps.
  • When changing DNS, update only the auth subdomain (auth.example.com) and monitor propagation. Use your DNS provider’s API for audited changes.
• Traffic steering: Use a traffic manager or load balancer to split traffic to a healthy POP or backup provider. Tie steering decisions to your edge health and steering playbooks.
• Multi‑CDN cutover: If you have active standby CDN, perform a staged cutover with health checks and route a small percentage first. Multi‑CDN and active‑standby patterns are documented in our edge host and multi‑vendor notes.

60–180 minutes: Validation and expand recovery

• Run full authentication test suites across regions and device types, including SSO flows, token exchange, refresh tokens and MFA challenges. Keep these tests integrated with your SRE validation suites.
• Monitor security telemetry closely for unusual patterns (mass password resets, elevated failed logins, new device enrollments) indicating fraud attempts after an outage. Tie such alerts to password hygiene and rotation workflows.
• Coordinate with vendor support—capture the vendor incident ID and escalate with evidence (timed logs, packet captures where permitted). Use your edge decision plane notes from edge auditability to guide escalation and evidence collection.

Customer and stakeholder communication

Clear status updates reduce customer frustration and regulator risk (GDPR/CCPA requirements around availability notices are evolving in 2026). Use the following cadence:

1. Initial update (within 15 minutes): Confirm you are aware, who is working it, scope (login issues), and ETA for next update.
2. Status updates (every 15–30 minutes): Actions taken, what’s mitigated, what remains impacted.
3. Resolution notice: What changed, whether credentials or tokens were rotated, and recommended customer actions (if any).
4. Postmortem announcement: When the RCA is available and what remediation steps are being implemented.

Sample message (public status):

We are investigating an issue affecting customer sign‑ins and SSO. Our operations team has identified a problem with an edge provider and is implementing a controlled failover. We will provide an update by 14:30 UTC. — Status Team

Security guardrails while failing over

• Do not disable logging or obscure audit trails during an outage—those logs are critical for postmortem and fraud detection.
• Avoid exposing origin APIs to the public internet without IP allowlists or mTLS. If you must, restrict the window and rotate any exposed credentials immediately after restoring the CDN. See mTLS and edge authorization patterns in edge authorization guidance.
• Monitor for credential stuffing and unusual token use. Consider temporarily hardening rate limits on authentication endpoints and integrating with automated password hygiene systems.
• If you suspect data was exposed during the outage or mitigation actions (for example, origin opened to the internet), consult legal and compliance immediately for notification obligations.

Restoring the CDN safely

1. Coordinate with the CDN vendor to understand the root cause and the fixes applied.
2. Reintroduce the CDN in stages: route a small subset of auth traffic back through the CDN, validate, then scale up. Use your edge decision plane to control phased rollouts.
3. After full cutover, run a stability window (24–72 hours) with increased synthetic checks and scheduled reviews for regressions. Keep these checks within your SRE observability suite.
4. Rotate any tokens or TLS keys that were modified or exposed during the incident as a precaution. Tie rotations to your credential automation and password hygiene playbooks.

Postmortem: structure and checklist

Run a blameless postmortem no later than 72 hours after incident closure. Include this checklist:

• Timestamps: timeline of events with exact UTC times for detection, mitigation steps, and vendor communications.
• Root cause analysis (5 Whys + evidence): network traces, vendor logs, and our telemetry that show chain of failure.
• Impact analysis: number of users affected, SLO breaches, revenue or compliance impact, support volume.
• Action items: prioritized remediation (short/medium/long‑term), owners, and target dates—examples below.
• Test & validation plan: how we’ll validate each remediation (synthetics, chaos tests, tabletop exercises). Align these with your SRE tabletop and chaos programs.
• Vendor SLA & contract review: escalate for credits or stricter SLAs if appropriate, and document support escalation effectiveness.
• Runbook updates: incorporate what worked, what failed, and precise commands or automation that should be codified. Store updates in the same repo as your incident response template.

Example action items (post‑incident)

• Implement multi‑CDN and automate health‑based steering for auth subdomains — owner: Network, due: 4 weeks. See multi‑vendor and pocket edge patterns at pocket edge hosts.
• Set DNS TTL to 60s for auth subdomains and add preconfigured DNS scripts to the incident runbook — owner: Platform, due: 1 week.
• Add origin allowlist + mTLS for direct origin access and document emergency cert rotation steps — owner: Security, due: 2 weeks. Refer to edge authorization guidance: edge authorization.
• Create a synthetic SSO smoke test matrix (regions, protocols, MFA) and add to incident monitoring — owner: SRE, due: 3 days. Integrate into the SRE synthetic suite.
• Run quarterly tabletop exercises with vendor escalation drills — owner: Incident Manager, due: ongoing. Use templates from the incident response template to standardize drills.

Quick reference checklist (one‑page)

• Confirm outage & open incident channel
• Assign roles and set update cadence
• Collect failure artifacts (curl, logs, header dumps) — keep them with your incident artifacts
• Temporarily disable edge features that block auth
• Bypass CDN for auth paths or DNS failover to backup
• Validate auth flows and monitor for fraud
• Communicate status externally and internally
• Reintroduce CDN gradually and validate
• Complete blameless postmortem and remediation plan

Practical commands & snippets (examples)

Use these to collect evidence quickly. Adapt to your environment and IaC.

• Check OIDC discovery: curl -i https://auth.example.com/.well-known/openid-configuration
• Check token endpoint: curl -v -X POST https://auth.example.com/oauth/token -d 'grant_type=client_credentials' -u client:secret
• Inspect DNS: dig +short auth.example.com and dig +trace auth.example.com
• Trace TLS chain: openssl s_client -connect auth.example.com:443 -showcerts

Case study snapshot: lessons from a 2026 edge outage

During a January 2026 multi‑provider edge disruption, several platforms observed that SSO failed because the CDN returned cached, truncated JSON for /.well‑known endpoints and stripped security headers. Teams that succeeded quickly had three things in place: (1) auth subdomain DNS TTLs of 60 seconds, (2) a preconfigured origin allowlist with mTLS, and (3) automated synthetic auth tests in several regions. Teams that struggled were tied to a single CDN and had hard‑coded endpoints in client apps, making emergency DNS changes ineffective. See practical notes on phased edge reintroduction in edge auditability and small-origin patterns at pocket edge hosts.

Future trends and recommendations for 2026+

• Adopt multi‑vendor edge strategies: multi‑CDN and edge federation will be mandatory for high‑availability identity in 2026. See multi‑vendor patterns in our pocket edge notes.
• Standardize auth subdomain patterns: separate auth subdomains (auth.example.com) from app content to reduce blast radius.
• Improve synthetic observability: global, protocol‑aware synthetic checks that exercise SSO, token refresh and MFA are now baseline. Integrate these into your SRE observability.
• Automate vendor failover: scripted DNS and CDN configuration via API reduce human error and shorten MTTR. Use edge decision plane principles from edge auditability.
• Run vendor outage drills: treat vendor failure like a first‑class scenario in your chaos program and use incident templates such as the one at filed.store.

"Prepare for supplier failure: your identity stack depends on the edge—design for graceful degradation, not surprise." — Incident Lead

Final checklist before closing an incident

• All auth functions validated end‑to‑end across regions.
• Token or credential rotations performed if origin exposure occurred. Follow credential automation and password hygiene playbooks.
• Public status updated to resolution and promised postmortem date committed.
• Action items logged, owners assigned, and follow‑ups scheduled.

Conclusion and call to action

Third‑party CDN and security provider outages are a clear operational risk for identity. The practical steps in this runbook—prepare, detect, triage, fail over, secure, and postmortem—reduce mean time to restoration while preserving user safety and regulatory compliance. Start by inventorying your auth dependencies this week: set DNS TTLs, codify direct origin access with mTLS, and add protocol‑aware synthetic checks. Make the runbook executable and run tabletop drills quarterly.

Next step: Download our incident runbook template and automated DNS failover scripts (updated for 2026) to implement these controls in your environment. If you’d like a peer review of your runbook, contact our platform reliability team for a 1:1 runbook audit.

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