Migrating from Auth0 to FusionAuth: A 60-Day Runbook

Teams move from Auth0 to FusionAuth for one dominant reason: to remove per-MAU cost by self-hosting (or running FusionAuth Cloud) while keeping most of the feature breadth they had. The trade is operational ownership. This runbook covers the 60-day path for a typical mid-market deployment. It is FusionAuth-specific; for the general managed-to-self-hosted case across Keycloak, Zitadel, and Ory, see the Auth0 to self-hosted playbook, and for the broader switching decision the Auth0 alternatives guide.

Verify before you act. Auth0's export policies and FusionAuth's feature names change. Confirm the password-hash export path for your current Auth0 plan and the current FusionAuth Import API behavior against live docs before committing the plan below. The single biggest planning risk is assuming you can bulk-export password hashes when your plan cannot.

Phase 1, Discovery and inventory (10 days)

Migration timelines track Action complexity and credential-export options, not user count. Inventory both before estimating.

Auth0 inventory. Every Action, Rule, and Hook in production, with the external services each calls and the stage it runs in (pre-registration, post-login, machine-to-machine). Every custom database connection. Every Enterprise Connection (SAML/OIDC) if you are multi-tenant. Your Auth0 Organizations structure if you use it for B2B. Every custom claim and metadata field the application reads from tokens. Every Management API integration in admin tooling.

The credential question (decide this first). Auth0 provides automated bulk user export, but password hashes are not part of the standard self-serve export; obtaining them generally requires a support request and is restricted by plan tier. This single fact determines your import strategy:

• If you can get the bcrypt hashes: plan a bulk import with credentials (Phase 3, path A). Users never notice.
• If you cannot: plan a just-in-time migration (Phase 3, path B), where users are migrated on their next successful login. Budget a longer dual-running window so the long tail of inactive users drains.

What does not migrate, plan to re-establish. Refresh tokens and active sessions (users re-authenticate at cutover). WebAuthn passkeys are bound to the relying-party ID and origin and cannot be transferred; users re-enroll. MFA enrollments (TOTP secrets) migrate only if you can export them, which is subject to the same export limits as hashes; otherwise users re-enroll MFA.

Phase 2, Stand up FusionAuth and model the tenant (14 days)

Deploy FusionAuth in a production-grade configuration (your Kubernetes cluster, VM fleet, or FusionAuth Cloud) with managed Postgres, Elasticsearch or OpenSearch for search, backups, and observability wired in.

Map the Auth0 model to FusionAuth.

• Auth0 Applications map to FusionAuth Applications; an Auth0 Tenant maps to a FusionAuth Tenant. Configure OAuth grants, redirect URIs, and token settings per application.
• Actions and Rules become FusionAuth Lambdas bound to the equivalent lifecycle events (JWT populate, registration validation, and so on). This is where most engineering time goes; budget for it deliberately. Re-implement each inventoried Action as a Lambda and unit-test the token output.
• For B2B tenancy, decide how Auth0 Organizations map: FusionAuth multi-tenancy via Tenants and Applications, or its Entity model, depending on your isolation needs. Confirm the mapping against current FusionAuth multi-tenancy docs; this is the part most likely to differ from your Auth0 layout.
• Recreate social and enterprise identity providers (Google, SAML, OIDC) and validate each login round-trip.
• Configure JWT signing keys and ensure the application validates FusionAuth's issuer, audience, and claims. Custom claims that Actions injected must be reproduced by Lambdas.

Phase 3, User and credential import (14 days)

Path A, bulk import with hashes (preferred). Use the FusionAuth Import API (/api/user/import), which accepts users in bulk along with their existing password hashes. FusionAuth supports common schemes including bcrypt (Auth0's default); set the hashing scheme, factor, and salt correctly per record so existing passwords validate without a reset. Import in batches, verify counts, and spot-check logins against known credentials in staging before any production import.

Path B, just-in-time migration (when hashes are unavailable). Stand up a migration path where, on a user's first login against FusionAuth, their credentials are validated against Auth0 (via a FusionAuth Connector or a custom authentication shim), and on success the password is captured and rehashed into FusionAuth. Active users migrate transparently as they log in; the inactive tail is handled by a forced password reset near the end of the dual-running window.

Either path: import user metadata, roles, registrations per application, and email-verified status so users do not get re-prompted unnecessarily.

Phase 4, Dual-run and validation (14 days)

Run FusionAuth alongside Auth0 and route a growing share of traffic to it (internal users, then a canary percentage, then the bulk). Validate on every critical flow: registration, login by each method, MFA challenge and step-up, password reset, social and enterprise SSO, token claims consumed by the app, and the Management-API-equivalent calls in your admin tooling. Compare token contents field by field against the Auth0 baseline. Watch error rates and latency; this is the window to find the Lambda or claim mismatch that a test suite missed.

Phase 5, Cutover and Auth0 decommission (8 days)

Flip the default to FusionAuth, keep Auth0 in read-only standby for a short rollback window, then decommission. At cutover, users re-authenticate (refresh tokens did not migrate) and re-enroll passkeys; communicate this in advance. After the standby window, export and archive Auth0 logs for your audit trail, revoke Auth0 API credentials, and close the tenant. Run a post-migration audit: confirm every inventoried Action has a working Lambda equivalent, every connection is live, and MFA and passkey re-enrollment rates are tracking as expected.

The gotchas, in one place

• Password hashes are the gating item. Confirm your Auth0 plan can export them before promising a no-reset migration; otherwise design for just-in-time migration plus a reset for the inactive tail.
• Passkeys cannot be migrated. They are bound to the relying-party origin; users re-enroll after cutover.
• Refresh tokens and sessions do not carry over. Everyone re-authenticates at cutover.
• Actions to Lambdas is the real work. It is logic re-implementation, not configuration, and it dominates the engineering estimate.
• Validate token claims field by field. The subtle breakage is a missing or differently-shaped claim the application silently depends on.