Compromised Password Detection

Overview

Compromised-password reuse is an account-access risk on password-auth flows. I built checks at login and password-change time and planned the rollout around account-access safety.

What I built

At a high level, the detection path uses a compromised-password signal at login and password-change time. The rollout piece is where most of the care went. You cannot move an existing login population straight to hard blocks without creating avoidable access and support load.

I phased the rollout through a feature flag, starting with forced rotation on password change, moving to prompts on login, and ending with hard blocks. Each phase gave users runway to change the password before hard enforcement, reducing avoidable lockout risk.

Outcome

• Compromised-password detection shipped on the enforced login and password-change paths.
• The rollout created a warning and migration path for affected password-auth users before hard enforcement.
• The phased rollout informed later auth security rollouts by separating warning, migration, and hard-enforcement phases.

Building the check was the smaller engineering task; moving existing users through staged enforcement took months. For later security migrations, the access plan became part of the feature definition.