Best Practice #2: Beware of Switching from Anonymous to Logged-in State

When the same user transitions from an "anonymous" to a "logged-in" state, using feature flags presents a challenge: how to guarantee that the functionality experienced before and after login remains consistent.

For example, on many consumer platforms (e.g., e‑commerce sites), a visitor may see a 50% discount on a product that is controlled by a feature flag, add the item to the cart, and then log in to complete the purchase. The system must decide how to handle that discount after the login.

In B2C software, several strategies are available, and you need to choose the one that best fits your user‑experience goals.

If your application is primarily transactional and the consistency of feature flags across sessions is not critical, you might ignore the discrepancy. However, if your experiments involve pricing variations, maintaining consistency becomes essential, as you likely want the same price shown in every session for the same user.

When you deem flag consistency important, the technical solution is to create a visitor ID for each visitor and track it with a cookie, as illustrated below.

When the visitor logs in, immediately associate the visitor ID with the logged‑in user ID. It is advisable to set the cookie’s expiration to a semi‑permanent duration to ensure a consistent experience throughout the lifecycle of any feature flag.