- A
Device code grant
Why wrong: Device code is for devices with limited input, not typical mobile apps.
- B
Client credentials grant
Why wrong: Client credentials grant is for server-to-server, not mobile apps.
- C
Implicit grant
Why wrong: Implicit grant is deprecated and less secure.
- D
PKCE
PKCE provides a secure authorization flow for public clients.
Question 33 of 1,000
CISSP Identity and Access Management Practice Question
This CISSP practice question tests your understanding of identity and access management. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A developer is implementing OAuth 2.0 for a mobile app (public client) that needs to access a user's data from a third-party API. To mitigate the authorization code interception attack, which OAuth 2.0 extension should be used?
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
✓
PKCE
PKCE (Proof Key for Code Exchange) is designed for public clients to prevent interception of the authorization code.
Key principle: Authentication proves identity; authorization controls what that identity can do after login. Both must work for full privileged access.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Device code grant
Why it's wrong here
Device code is for devices with limited input, not typical mobile apps.
- ✗
Client credentials grant
Why it's wrong here
Client credentials grant is for server-to-server, not mobile apps.
- ✗
Implicit grant
Why it's wrong here
Implicit grant is deprecated and less secure.
- ✓
PKCE
Why this is correct
PKCE provides a secure authorization flow for public clients.
Related concept
Authentication checks who the user is.
Common exam traps
Common exam trap: authentication is not authorization
Logging in proves the user can authenticate. It does not automatically mean the user is allowed to enter privileged or configuration mode. Watch for AAA authorization, privilege level and command authorization details.
Detailed technical explanation
How to think about this question
This kind of question is testing the difference between identity and permission. A user may successfully log in to a router because authentication is working, but still fail to enter configuration mode because authorization is missing, misconfigured or mapped to a lower privilege level.
KKey Concepts to Remember
- Authentication checks who the user is.
- Authorization controls what the user is allowed to do after login.
- Privilege levels affect access to EXEC and configuration commands.
- AAA, TACACS+ and RADIUS can separate login success from command access.
TExam Day Tips
- Do not assume successful login means full administrative access.
- Look for words such as cannot enter configuration mode, privilege level, authorization or command access.
- Separate login problems from permission problems before choosing the answer.
Key takeaway
Authentication proves identity; authorization controls what that identity can do after login. Both must work for full privileged access.
Real-world example
How this comes up in practice
A developer is choosing between AES-256 (symmetric) and RSA-2048 (asymmetric) for encrypting a large file that will be sent to a partner. Symmetric encryption is fast but requires key exchange; asymmetric is slower but solves the key distribution problem. A hybrid approach — encrypt the file with AES, encrypt the AES key with RSA — is standard. Questions like this test whether you understand when each approach applies.
What to study next
Got this wrong? Here's your next step.
Review Cisco AAA concepts — authentication, authorization, and accounting. Study privilege levels (0–15), command authorization under TACACS+, and how RADIUS differs. Then practise related CISSP questions on access control and AAA configuration.
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Identity and Access Management — study guide chapter
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FAQ
Questions learners often ask
What does this CISSP question test?
Identity and Access Management — This question tests Identity and Access Management — Authentication checks who the user is..
What is the correct answer to this question?
The correct answer is: PKCE — PKCE (Proof Key for Code Exchange) is designed for public clients to prevent interception of the authorization code.
What should I do if I get this CISSP question wrong?
Review Cisco AAA concepts — authentication, authorization, and accounting. Study privilege levels (0–15), command authorization under TACACS+, and how RADIUS differs. Then practise related CISSP questions on access control and AAA configuration.
What is the key concept behind this question?
Authentication checks who the user is.
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Last reviewed: Jul 4, 2026
This CISSP practice question is part of Courseiva's free ISC2 certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the CISSP exam.
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