PLATFORM MIGRATION
Preserving User Sessions Across a Platform Move
You chose a managed platform because shipping fast mattered more than owning every layer. That trade-off made sense—until it didn't. Now your authentication provider can rewrite terms overnight, your database answers to someone else's API, and your LLM access survives only as long as a vendor stays friendly. The risk is concrete: one policy change or account suspension can lock you out of your own users' data and force every customer to reset their credentials. Think of it like renting an apartment where the landlord holds your only set of keys—and can refuse to copy them when you move out.
The question isn't whether to migrate. It's how to move to self-hosted infrastructure without forcing your users to log in again.
To preserve user sessions during a platform migration, export your authentication data completely, configure your new system to honor existing tokens, and cut over traffic in a controlled sequence.
This guide follows time-based ordering: prepare your session data, configure your new authentication layer, execute the migration, and verify continuity. Each phase builds on the previous one. Skip steps and you trigger the forced logouts you're trying to avoid.
Export Session Data Before Changing Any Infrastructure
A seamless migration starts with a complete export of your existing session and authentication data. Without this data, you cannot honor active sessions on your new platform—every user faces a forced logout. You need to extract three categories of data.
Export user credential records with their original hash formats. This includes user identifiers, hashed passwords, email addresses, and any metadata your application uses for authorization decisions. Preserve the exact hash algorithm and salt structure so your new system can validate passwords without forcing resets. If you're running bcrypt with a cost factor of 12, your new system needs to know that—not guess.
Capture active session and token data with their expiration timestamps. Export refresh token mappings, device fingerprints used for security checks, and any session state your application maintains server-side. Miss this data and users holding valid sessions will appear unauthenticated the moment you switch platforms.
Extract cryptographic signing keys if your platform exposes them. If your existing platform uses JWT tokens, you need the exact signing secret or private key that validates those tokens. Without the original key, every token your users hold becomes invalid at cutover. Some managed services guard these keys jealously—they won't hand them over. In that case, plan for a brief re-authentication window during cutover and communicate it clearly to users beforehand.
Configure Your New System to Honor Existing Tokens
Your self-hosted authentication layer must accept tokens issued by the old platform while also issuing new tokens your application recognizes. This dual capability makes session preservation possible.
Configure token validation to use the same signing key you exported. Deploy your chosen self-hosted authentication solution and set it to verify tokens using the cryptographic material from your previous platform. This lets your new system accept pre-migration tokens without modification—users stay logged in without knowing anything changed.
Match token issuance to the old format exactly. When a user's token expires and they request a refresh, your new system must produce a token your application accepts without code changes. Match the algorithm (HS256 or RS256), the issuer claim, the audience claim, the expiration windows, and any custom claims your authorization logic depends on. A single mismatched claim can trigger rejection across your entire application.
Preserve existing identifiers when mapping user identity. Create an import process that maps old user identifiers to new records without changing the identifiers themselves. If your application stores user IDs in other tables—orders, preferences, content ownership—those references must remain valid after migration. Check that authentication succeeds and that data integrity holds—a user who logs in fine but sees someone else's order history indicates a mapping failure.
Cut Over Traffic Through a Staged Sequence
The actual migration moment demands careful orchestration. A rushed cutover can invalidate sessions even when your technical preparation is flawless.
Run parallel operation to validate your new system under real conditions. Keep both authentication systems running simultaneously, with your new self-hosted system fully operational and tested before you route any production traffic to it. Verify that you can create users, issue tokens, validate tokens, and refresh tokens without errors in the new environment.
Shift traffic gradually to limit exposure to problems. Start by routing 5% of authentication requests to your new system while monitoring for errors. If users report login failures or your error rates spike, route traffic back to the old system while you investigate. Increase the percentage only after each stage shows stable performance. In our migrations, we've found a progression of 5%, then 25%, then 50%, then 100% works well—with at least a few hours of observation between each jump. Your context may require different increments.
Maintain legacy token support to handle stragglers gracefully. After traffic is fully migrated, keep the ability to validate tokens issued by the old platform for a defined period—in our experience, two to four weeks typically suffices, depending on your longest refresh token lifetime. Some users may hold long-lived refresh tokens issued before migration. Your new system should honor these tokens until they naturally expire, at which point users receive new tokens from your self-hosted infrastructure.
Verify Continuity Through Systematic Testing
After cutover, systematic verification confirms your migration achieved its goal: users remain logged in without interruption.
Monitor error rates to catch systemic problems. Compare your authentication error rates to your baseline for the first 48 hours after migration. Pay particular attention to token validation errors, which indicate a mismatch between old tokens and new validation logic. If your baseline shows 0.1% authentication failures and you're suddenly seeing 2%, investigate immediately.
Run end-to-end journey tests to catch integration issues. Test the complete user experience from the perspective of someone who was logged in before migration. Confirm they can access protected resources without re-authenticating, refresh their session when their token expires, and log out and log back in successfully. Each flow exercises different parts of your authentication system. Automated tests help, but also walk through these journeys manually—you'll catch UX problems that scripts miss.
Collect user feedback to surface edge cases. Establish a clear channel for users to report authentication problems during the first week after migration. Automated monitoring catches broad failures, but individual users encounter edge cases—unusual token states, rare device configurations, timing-dependent issues—that only surface through direct reports. Treat each report as a signal to investigate, not an isolated incident. Three users reporting the same problem usually means thirty users experiencing it silently.
What Comes Next
Your migration succeeds or fails based on preparation. Four actions will ready you to execute:
- Audit your current platform to identify all session-related data and cryptographic keys you need to export. Document what's accessible and what's locked away.
- Set up a staging environment with your chosen self-hosted authentication solution and import a subset of user data to validate your migration process end-to-end.
- Create a rollback plan that lets you revert to your old platform within minutes if critical issues emerge during cutover.
- Schedule your migration during a low-traffic period and brief your support team on what questions to expect during the transition window.
The goal isn't just technical success—it's invisible success. Your users should wake up the next morning, open your app, and notice nothing at all. That silence is the sound of a migration done right.