The answer is the authorization code flow with PKCE. This is the correct choice because a single-page app (SPA) running in a browser cannot securely store a client secret, making the standard authorization code flow vulnerable to interception. PKCE (Proof Key for Code Exchange) mitigates this by requiring the app to generate a cryptographic code verifier and its transformed code challenge during the initial request; when the authorization code is later exchanged for tokens, the server verifies that the presenter possesses the original verifier, blocking code injection attacks even if the code is intercepted. On the AZ-204 exam, this scenario tests your understanding of secure authentication patterns for browser-based apps, often appearing as a trap where candidates mistakenly choose the implicit grant (now deprecated) or the client credentials flow. Remember the key distinction: PKCE uses a dynamically generated secret per request, not a static client secret. Memory tip: think “PKCE = Proof Key = Prove you have the key, no secret needed.”
AZ-204 Implement Azure security Practice Question
This AZ-204 practice question tests your understanding of implement azure security. 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.
A single-page app signs in users with Microsoft Entra ID and calls a protected API. The app cannot safely keep a client secret. Which OAuth flow should be used?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Authorization code flow with PKCE
The authorization code flow with PKCE (Proof Key for Code Exchange) is the recommended OAuth flow for single-page apps that cannot securely store a client secret. PKCE ensures that even if the authorization code is intercepted, it cannot be exchanged for tokens without the original code verifier, mitigating the risk of code injection attacks. This flow aligns with Microsoft's best practices for native and browser-based applications using Microsoft Entra ID.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Implicit flow
Why it's wrong here
Implicit flow is legacy and less secure than authorization code with PKCE.
✗
Client credentials flow
Why it's wrong here
Client credentials is for daemon/service-to-service access, not user sign-in in a SPA.
✗
Resource owner password credentials flow
Why it's wrong here
ROPC is discouraged and incompatible with many modern security controls.
✓
Authorization code flow with PKCE
Why this is correct
PKCE protects public clients that cannot store secrets and is recommended for SPAs.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse the implicit flow (which was historically used for SPAs) as still valid, but Microsoft and OAuth standards now mandate the authorization code flow with PKCE for all public clients, including single-page apps.
Detailed technical explanation
How to think about this question
Under the hood, PKCE uses a cryptographically random code verifier (a high-entropy string) and its SHA-256 hash (code challenge) sent during the authorization request. The authorization server stores the challenge, and when the client exchanges the code, it must provide the original verifier, which the server hashes and compares. This prevents authorization code interception attacks even without a client secret. In real-world scenarios, this flow is critical for SPAs using MSAL.js 2.0+ with Microsoft Entra ID, as it supports silent token renewal via iframes using the `prompt=none` parameter.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this AZ-204 question in full detail.
Implement Azure security — This question tests Implement Azure security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Authorization code flow with PKCE — The authorization code flow with PKCE (Proof Key for Code Exchange) is the recommended OAuth flow for single-page apps that cannot securely store a client secret. PKCE ensures that even if the authorization code is intercepted, it cannot be exchanged for tokens without the original code verifier, mitigating the risk of code injection attacks. This flow aligns with Microsoft's best practices for native and browser-based applications using Microsoft Entra ID.
What should I do if I get this AZ-204 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
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These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A single-page app signs in users with Microsoft Entra ID and calls a protected API. The app cannot safely keep a client secret. Which OAuth flow should be used? The design must avoid adding custom operational scripts.
hard
A.Implicit flow
B.Client credentials flow
C.Resource owner password credentials flow
✓ D.Authorization code flow with PKCE
Why D: The authorization code flow with PKCE (Proof Key for Code Exchange) is the recommended OAuth 2.0 flow for single-page applications (SPAs) that cannot securely store a client secret. PKCE uses a dynamically generated cryptographic code verifier and challenge, ensuring that even if the authorization code is intercepted, it cannot be exchanged for tokens without the original verifier. This flow is designed for public clients (like SPAs) and avoids the need for custom operational scripts.
Variation 2. A single-page app signs in users with Microsoft Entra ID and calls a protected API. The app cannot safely keep a client secret. Which OAuth flow should be used? The architecture review board prefers a managed AWS-native control.
hard
A.Implicit flow
B.Client credentials flow
C.Resource owner password credentials flow
✓ D.Authorization code flow with PKCE
Why D: The authorization code flow with PKCE (Proof Key for Code Exchange) is the correct choice because it is designed for public clients (like single-page apps) that cannot securely store a client secret. PKCE uses a dynamically generated cryptographic code verifier and challenge to prevent authorization code interception attacks, making it the recommended OAuth 2.0 flow for SPAs calling protected APIs in Microsoft Entra ID.
Variation 3. A single-page app signs in users with Microsoft Entra ID and calls a protected API. The app cannot safely keep a client secret. Which OAuth flow should be used? The team wants the control to be enforceable during normal operations.
hard
A.Implicit flow
B.Client credentials flow
C.Resource owner password credentials flow
✓ D.Authorization code flow with PKCE
Why D: The authorization code flow with PKCE (Proof Key for Code Exchange) is the recommended OAuth flow for single-page apps because it prevents the client secret from being exposed by using a dynamically generated code verifier and challenge. This flow ensures that even if the authorization code is intercepted, it cannot be exchanged for tokens without the original code verifier, making it secure for public clients that cannot safely store secrets.
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Question Discussion
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