The log file looked clean at first. Then the email addresses appeared, hanging there in plain text like open doors. In OpenID Connect (OIDC) systems, logs often capture sensitive user data—emails included. Left unmasked, they are an attack surface, a compliance risk, and a privacy violation waiting to happen.
Masking email addresses in logs is not optional. It is a deliberate act that starts at the point where identity data flows through your OIDC pipeline. Every debug trace, request log, or audit entry is a potential leak. The fix is straightforward: intercept and transform before storage.
Identify where email data enters your logs
OIDC responses can carry email addresses in ID tokens, claims, or userinfo API calls. These values often pass through authentication handlers, middleware, or logging frameworks. Search these layers for logging statements that call these values directly.
Implement masking at the logging layer
Modify log formatters to detect strings matching email patterns. Replace the local part (before the @) with a fixed mask like *** or a hash. Preserve domain names if needed for troubleshooting. Use regex-based filtering to enforce the mask. For high-performance services, apply masking in memory, before serialization.