Quick Answer
The answer is the Authorization Code Grant with PKCE. This is the most appropriate OAuth 2.0 grant type for a mobile app because mobile applications are public clients that cannot securely store a client secret, making them vulnerable to authorization code interception attacks. PKCE mitigates this by replacing the static client secret with a dynamically generated code verifier and its SHA-256 hash, the code challenge; the authorization server verifies the code verifier against the challenge before issuing tokens, ensuring that even if the authorization code is stolen, it cannot be exchanged without the original verifier. On the CISSP exam, this scenario tests your understanding of the OAuth 2.0 Security Best Current Practice (BCP) for native apps, often appearing as a trap where candidates mistakenly choose the Implicit Grant, which is now deprecated for mobile use. Remember the memory tip: “PKCE protects public clients from code interception by proving possession of the verifier.”
This CISSP practice question tests your understanding of identity and access management. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
An organization uses OAuth 2.0 for delegated access to APIs. A developer creates a public client application that runs on mobile devices. Which OAuth 2.0 grant type is MOST appropriate for this scenario?
Client Credentials Grant
Why wrong: Used for machine-to-machine, not user delegation.
Implicit Grant
Why wrong: Deprecated; less secure for mobile apps.
Resource Owner Password Credentials Grant
Why wrong: Not recommended; requires direct credential handling.
Authorization Code Grant with PKCE
Provides secure token exchange for public clients.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Authorization Code Grant with PKCE
The Authorization Code Grant with PKCE (Proof Key for Code Exchange) is the most appropriate for a public client on a mobile device because it prevents authorization code interception attacks. PKCE replaces the client secret with a dynamically generated code verifier and challenge, ensuring that even if the authorization code is intercepted, it cannot be exchanged for tokens without the original verifier. This is the OAuth 2.0 Security Best Current Practice (BCP) recommendation for native and mobile apps.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Client Credentials Grant
Why it's wrong here
Used for machine-to-machine, not user delegation.
Implicit Grant
Why it's wrong here
Deprecated; less secure for mobile apps.
Resource Owner Password Credentials Grant
Why it's wrong here
Not recommended; requires direct credential handling.
Authorization Code Grant with PKCE
Why this is correct
Provides secure token exchange for public clients.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
The trap here is that candidates often choose the Implicit Grant (Option B) because they mistakenly believe it is simpler for mobile apps, but the CISSP exam tests the current OAuth 2.0 Security BCP which deprecates Implicit and mandates PKCE for public clients.
Detailed technical explanation
Under the hood, PKCE works by having the client generate a cryptographically random 'code_verifier' (a high-entropy string) and its SHA-256 hash as the 'code_challenge' sent with the authorization request. When exchanging the authorization code, the client sends the original 'code_verifier', which the authorization server verifies against the stored challenge, effectively binding the code to that specific client session. In real-world scenarios, this prevents attacks where a malicious app on the same device intercepts the authorization code via URI scheme hijacking or other side channels.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
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FAQ
Identity and Access Management — This question tests Identity and Access Management — Read the scenario before looking for a memorised answer..
The correct answer is: Authorization Code Grant with PKCE — The Authorization Code Grant with PKCE (Proof Key for Code Exchange) is the most appropriate for a public client on a mobile device because it prevents authorization code interception attacks. PKCE replaces the client secret with a dynamically generated code verifier and challenge, ensuring that even if the authorization code is intercepted, it cannot be exchanged for tokens without the original verifier. This is the OAuth 2.0 Security Best Current Practice (BCP) recommendation for native and mobile apps.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 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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