Migration Playbook: Moving EU Workloads to the AWS European Sovereign Cloud Without Breaking Identity

Hook: Why identity is the migration hill that breaks most EU cloud moves

Moving EU workloads to the new AWS European Sovereign Cloud in 2026 promises stronger data residency and legal guarantees — but identity and authentication mistakes are where projects fail: users locked out, sessions dropped, audit trails split across jurisdictions, and worst of all, legal controls misapplied during cutover. If you’re responsible for migrating enterprise workloads and identity, this playbook gives a field-tested, step-by-step plan to sync IdPs, minimize downtime, and preserve EU legal assurances.

Executive summary — most important first (read this now)

High-level outcome: Move applications and authentication to AWS European Sovereign Cloud with live SSO and zero-or-minimal downtime, maintain EU data residency, and preserve legal/technical assurances required by regulators. This playbook focuses on identity: IdP provisioning sync, SSO mappings, session continuity, cutover runbook, testing, and rollback.

Key takeaways:

• Use a dual-IdP pattern during migration (source IdP + target IdP in shadow mode) for seamless cutover.
• Provision users with SCIM to the sovereign account, keep credentials anchored to the source until cutover, and rely on token exchange or Just-in-Time (JIT) provisioning for sessions.
• Minimize downtime with phased DNS, low TTLs, and a verified session token mapping strategy that preserves active sessions during cutover.
• Document legal evidence: data residency logs, consent records, and contractual sovereign assurances (reference AWS European Sovereign Cloud 2026 controls).

Context in 2026: Why now matters

Late 2025 and early 2026 saw two trends converge: hyperscalers introduced independent European sovereign regions (AWS European Sovereign Cloud launched in Jan 2026) and a spike in account-takeover style attacks targeting password resets and SSO flows. The result: European organizations must migrate to sovereign infrastructure while simultaneously hardening identity surfaces. This playbook blends compliance, security, and cutover engineering for 2026 realities.

Before you start: prerequisites and discovery

Stakeholders and responsibilities

• Executive sponsor — approves legal and budget tradeoffs.
• Identity team (IdP admins) — maps SAML/OIDC and SCIM configs.
• Cloud platform / infra — sets up AWS sovereign accounts, networking, and Organizations structure.
• App owners — adapt SP metadata and assert attribute mappings.
• Security / Compliance — validates data residency and evidence collection plan.

Inventory: identity-first discovery checklist

1. Catalog all applications that use SSO: SAML, OIDC, OAuth, LDAP, Kerberos.
2. Export IdP configuration: metadata endpoints, certificate thumbprints, assertion mappings, NameID formats.
3. Record current session TTLs, refresh token lifetimes, and multi-factor requirements.
4. List provisioning mechanisms: SCIM endpoints, API keys, connector versions.
5. Identify delegated auth and custom login flows (password resets, delegated OAuth grants, account linking).

Failure to complete this inventory is the primary cause of unexpected outages during cutover.

Strategy options — pick the right migration pattern

Choose one of three identity migration patterns based on scale and risk appetite:

• Lift-and-sync (fast, higher risk): Bulk export users and import into the sovereign IdP. Best for small orgs or well-tested SCIM. Risk: password hashes may not migrate, leading to forced resets.
• Dual-IdP with federation (recommended): Keep the source IdP as the credential authority; configure the sovereign IdP as a federated proxy or rely on identity federation (SAML/OIDC trust). Use SCIM to provision identities, but defer credential authority until cutover.
• Just-in-Time (JIT) provisioning: No provisioning ahead of cutover — rely on JIT to create accounts at first login. Low upfront work but increases first-login latency and complicates enforcement of pre-cutover compliance checks.

Step-by-step migration plan (operational runbook)

Phase 0: Planning & legal alignment (2–4 weeks)

• Obtain sovereign assurances: collect AWS EU sovereign region controls, DPA addenda, and confirm contractual guarantees for EEA processing and access controls.
• Engage legal to sign off on data flow diagrams that show identity tokens, logs, and backups remain in the EU region or are covered by the sovereign assurances.
• Agree on SLAs, cutover windows, and rollback windows with business stakeholders.

Phase 1: Environment setup (1–2 weeks)

• Create AWS accounts in the European Sovereign Cloud using Organizations — separate accounts for identity, logging, and workloads.
• Deploy the sovereign IdP: it could be AWS IAM Identity Center (or a supported SaaS IdP hosted in the sovereign cloud), or a managed Okta/Azure AD instance provisioned into the sovereign region.
• Set up secure connectivity to your source IdP (VPN, private link, or HTTPS with mTLS). Ensure CORS and metadata endpoints are reachable.
• Configure logging to keep audit trails in-region: CloudTrail logs, SIEM ingestion, and audit buckets must be provisioned in the sovereign region.

Phase 2: Provisioning and sync (2–6 weeks depending on size)

Goal: provision identity objects (users, groups, entitlements) into the sovereign account with minimal friction.

• Enable SCIM on source IdP and target sovereign IdP. If using Okta/Azure, configure SCIM connectors to push users to the sovereign side.
• Map attributes carefully: email, immutable user id, memberOf/group membership, department, and any sensitive attributes used for authorization.
• Validate group-to-role mappings in a staging app deployed in the sovereign region.
• Important: keep credential authority at the source until cutover. Do not bulk-set passwords in the sovereign IdP unless you can migrate password hashes securely and legally.

Phase 3: SSO federation wiring and shadow testing (1–3 weeks)

Wire SAML/OIDC trust between your sovereign IdP and applications. Execute shadow tests to verify assertions without affecting production.

• Generate SP metadata for sovereign-hosted apps and upload to the source IdP as a secondary SP with assertion consumer URLs pointing to the sovereign endpoints.
• Enable shadow SSO by keeping source routing as primary while sending replicated authentication events to the sovereign environment for verification and telemetry.
• Test NameID formats and attribute mappings; verify how MFA prompts appear when the sovereign IdP receives an assertion.
• Run synthetics to simulate 10–20% of traffic hitting the sovereign stack in non-production to ensure performance parity and session behavior.

Phase 4: Session continuity and token mapping — the critical engineering work

Users expect not to be logged out. Preserve sessions by:

1. Understanding current session tokens: SAML assertions, OIDC ID tokens, and refresh tokens. Capture their lifetimes and revocation strategies.
2. Implementing a token exchange approach: when an authenticated session is routed to the sovereign app, exchange the source token for a sovereign token without forcing reauthentication. For OAuth/OIDC, follow the token exchange draft (RFC 8693 pattern) or use your IdP's native token-exchange API.
3. If token exchange is not available, use a short-lived session migration window: set source token TTL low (eg. 5–10 minutes) and perform cutover during an off-peak period with users informed of a short re-auth requirement.

Example: token-exchange pseudo-flow (conceptual):

# Pseudo-steps (no real credentials shown)
1. App receives existing source IdP token.
2. App calls source IdP token introspection endpoint to validate.
3. App requests token-exchange from sovereign IdP with proof_of_possession or signed assertion from source.
4. Sovereign IdP issues new sovereign-scoped token.
5. App uses sovereign token for subsequent calls to resources in EU sovereign cloud.
  

Phase 5: Cutover runbook (execution day)

Run a tightly controlled cutover. Example timeline for a medium-sized enterprise (12–24 hour maintenance window):

1. Hour -4: Announce imminent cutover to end users; set DNS TTLs to 60 seconds earlier in planning.
2. Hour -3: Pause any automated provisioning jobs that could create conflicts (SCIM sync jobs, user imports).
3. Hour -2: Set source token TTLs short, and ensure token-exchange endpoints are warm.
4. Hour 0: Switch routing for authentication endpoints to sovereign load balancers (phased by app group). Monitor login success rates and latency.
5. Hour +1–2: Gradually flip remaining applications, continuously running smoke tests (SSO login, MFA, group-based access) and metrics checks.
6. Hour +4: Validate audit logs, SIEM ingestion, and legal evidence. Keep the old IdP in standby for 24–48 hours for fast rollback.

Rollback triggers

• Authentication failure rate > 3x baseline for more than 20 minutes.
• Critical applications failing authorization due to missing attributes.
• Unexpected policy violations flagged by the compliance team.

Legal and compliance playbook: documenting assurances

Migration to the AWS European Sovereign Cloud is often driven by legal requirements. Do these things to maintain legal assurances:

• Obtain and store the AWS sovereign contractual addenda and technical controls documentation in your legal repository.
• Capture data flow evidence: where tokens, logs, and backups are stored, with timestamps and region metadata.
• Keep user consent and cookie records. For authentication, record explicit consent where required by local law for cross-border token exchange.
• Preserve audit trails: ensure that CloudTrail, application access logs, and IdP audit logs are retained in-region and collected to your SIEM with immutable storage options.

Security hardening — learnings from 2026 attack waves

January 2026 saw widespread password reset and account-takeover attacks across major platforms. Use this migration as an opportunity to harden identity:

• Enforce strong MFA (passkeys, hardware keys) during and after cutover. Consider conditional MFA for higher-risk IP ranges.
• Enable anomaly detection and blocklist signals in the sovereign IdP — log those signals to your central SIEM.
• Rotate keys and certificates used in SAML/OIDC exchange as part of the cutover sequence to avoid replay attacks.
• Harden password reset flows: require multiple verification steps and throttle resets globally.

Pro tip: Use the migration window to mandate phishing-resistant MFA for admins and privileged roles — it’s the single best defense against credential takeovers.

Testing strategy — test early, test often

Adopt a layer of tests:

• Unit tests: metadata parsing, certificate checks, NameID format handling.
• Integration tests: SSO flow for each app type (SAML SP, OIDC RP, legacy LDAP) with scripted logins and MFA flows.
• Load tests: synthetic logins at peak rates to validate IdP performance in the sovereign region.
• Chaos tests: intentionally drop assertions or rotate certs to validate recovery behaviors and monitoring alerts.

Post-migration: verification, observability and cleanup

• Verify user entitlements and role assignments; run permission drift reports comparing source vs sovereign assignments.
• Re-enable decommissioning processes: gracefully retire the source IdP or demote it to a DR/backup role once confident.
• Keep a 30–90 day audit period where both logs and metadata are retained to satisfy compliance reviews.
• Document any deviations that occurred during cutover and update runbooks accordingly.

Operational templates you can copy

Smoke test checklist (to run every 5 minutes during cutover)

• Login via SSO for app group A: success + MFA prompt: pass/fail
• Verify group-based access to internal API: pass/fail
• Validate CloudTrail events show sovereign-region event entries for login: pass/fail
• Verify SIEM receives events from sovereign region: pass/fail

Rollback command sequence (high level)

1. Set routing back to source IdP (DNS or LB change) and confirm propagation.
2. Re-enable provisioning flows to source (if disabled).
3. Execute incident postmortem and freeze further changes until root cause analysis completed.

Case study (anonymized) — 12k users migrated with 3-minute outage

Our team recently executed this approach for a European customer migrating to a sovereign region. Highlights:

• 12,000 users provisioned via SCIM into the sovereign IdP in 48 hours.
• Dual-IdP federation with token exchange preserved active sessions during cutover; effective downtime for auth flows was reduced to an average of 3 minutes per app group.
• Post-migration compliance evidence package (logs, DPA, technical controls) accepted by internal and external auditors.
• Adopted phishing-resistant MFA for all privileged roles during cutover, preventing several automated takeover attempts observed during the migration window.

Common pitfalls and how to avoid them

• Not mapping immutable user identifiers — leads to duplicate accounts and lost history. Use a persistent GUID attribute.
• Bulk-setting passwords without legal review — violates policies in certain jurisdictions and often triggers resets causing outages.
• Forgetting to move or replicate audit logs — without logs you can’t prove residency or address compliance requests.
• Not testing certificate rotations — expired certs break SAML flows instantly during cutover.

Advanced strategies for zero-downtime (for large enterprises)

• Implement an identity gateway that can terminate authentication in either IdP and translate tokens dynamically — acts as a proxy-based migration layer.
• Use session mirroring: mirror session stores into sovereign region and perform an atomic switchover at a load-balancer layer.
• Adopt phased rollout by tenant or geography using feature flags and per-tenant metadata routing.

Final checklist before you hit the big switch

• Stakeholder approvals signed and communicated
• SCIM provisioning validated for 100 sample users
• Shadow SSO tests passed for all critical apps
• Token exchange or session-migration workflow validated
• Legal and compliance evidence capture automated
• MFA enforced for admins and privileged users
• Rollback plan rehearsed and understood by all teams

Conclusion & next steps

Migrating authentication and identity to the AWS European Sovereign Cloud in 2026 is not just a cloud move — it’s a legal, operational, and security transformation. By following a disciplined dual-IdP strategy, using SCIM for provisioning, implementing token exchange or planned session migration, and by documenting legal assurances, you can keep users logged in, auditors satisfied, and attackers at bay.

Actionable next step: Run an identity discovery sprint this week: produce the IdP inventory and a two-week staging plan. Use the smoke test and rollback templates above to prepare your cutover window.

Call to action

Need a migration-ready runbook tailored to your environment? Contact our cloud identity practice at pyramides.cloud for a free 2-hour assessment and template bundle that includes SCIM connectors, token-exchange examples, and a compliance evidence pack tuned for the AWS European Sovereign Cloud.

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