CAS-004 Security Engineering Practice Question
A security administrator is troubleshooting a web application that intermittently rejects valid user sessions. Logs show the application server's clock drifted several minutes behind the authentication service, and the tokens carry short validity windows with issued-at and expiry claims. Which action MOST directly resolves the intermittent rejections?
⚠ Common exam trap
The trap here is reaching for token lifetime or validation changes to stop the errors instead of correcting the clock skew that makes correct validation fail.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Configure the application server and authentication service to synchronize their clocks with the same trusted NTP time sources.
Time-based token claims are only meaningful when the issuer and validator share a common time reference. Synchronizing both systems to the same authenticated NTP sources eliminates the skew that causes valid tokens to be judged expired or not yet valid, fixing the rejections without loosening token lifetimes or removing expiry enforcement.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Increase the token validity window from five minutes to several hours so clock differences no longer matter.
Why it's wrong here
Widening the validity window masks the symptom by making tokens acceptable for longer, but it substantially increases the exposure window if a token is stolen and does nothing to correct the underlying time disagreement. The authentication service and application server would still disagree about when tokens were issued, and other time-sensitive operations remain broken.
- ✗
Disable expiry claim validation on the application server so tokens are trusted until the session store marks them invalid.
Why it's wrong here
Ignoring the expiry claim removes a core control that bounds the usefulness of a stolen token, effectively converting short-lived credentials into long-lived ones. It also leaves the clock disagreement in place, which will resurface in audit logs, certificate validation, and any other time-dependent check the application performs.
- ✓
Configure the application server and authentication service to synchronize their clocks with the same trusted NTP time sources.
Why this is correct
Token validation compares the issued-at and expiry claims against the validator's own clock, so a multi-minute skew causes tokens that are genuinely valid to appear not-yet-valid or expired. Pointing both systems at the same authenticated NTP hierarchy removes the skew at its source and restores consistent validation without weakening token lifetimes.
- ✗
Shorten the token validity window further so that affected tokens expire quickly and users reauthenticate more often.
Why it's wrong here
Shrinking the lifetime makes the problem worse because a validator whose clock lags will consider even freshly issued tokens to be not yet valid, increasing rejection frequency. This approach punishes users with more frequent logins while the root cause, unsynchronized system clocks, remains entirely unaddressed.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official CompTIA exam blueprint
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