The answer is to deploy Microsoft Entra Application Proxy with pre-authentication. This approach is correct because Application Proxy acts as a reverse proxy for on-premises legacy apps that use outdated authentication protocols, allowing them to be published securely to the cloud. By enabling pre-authentication, the proxy forces all incoming requests to authenticate first through Microsoft Entra ID, which then seamlessly applies SSO and enforces MFA policies—all without any modification to the application’s source code. On the Microsoft Cybersecurity Architect exam, this scenario tests your understanding of how to bridge legacy authentication gaps using cloud-native tools; a common trap is choosing Conditional Access alone, which fails because legacy protocols lack the modern auth headers needed to enforce MFA. Another pitfall is selecting MSAL, which requires code changes the vendor hasn’t provided. Remember the memory tip: “Proxy pre-auth, no code to wrench—SSO and MFA on the legacy bench.”
SC-100 Design security solutions for infrastructure Practice Question
This SC-100 practice question tests your understanding of design security solutions for infrastructure. 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.
You are designing a secure access solution for an on-premises application that uses legacy authentication protocols. The organization plans to migrate to Microsoft Entra ID but the application vendor has not yet provided a modern authentication update. The solution must enable single sign-on (SSO) and support multifactor authentication (MFA) for this application without modifying the application code. Which approach should you recommend?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Deploy Microsoft Entra Application Proxy with pre-authentication
Option C is correct because Microsoft Entra Application Proxy allows publishing on-premises apps with legacy authentication, and it can integrate with Entra ID for pre-authentication, enabling SSO and MFA without code changes. Option A is wrong because Entra ID Conditional Access policies require modern authentication to enforce MFA. Option B is wrong because the Microsoft Authentication Library (MSAL) requires app code changes. Option D is wrong because federation with ADFS still requires modern auth at the app level.
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.
✗
Integrate the application with the Microsoft Authentication Library (MSAL)
Why it's wrong here
MSAL requires code changes to the application.
✗
Federate the on-premises Active Directory with Microsoft Entra ID
Why it's wrong here
Federation alone does not enable MFA for legacy apps that do not support modern auth.
✗
Use Microsoft Entra Conditional Access policies to require MFA
Why it's wrong here
Conditional Access requires modern authentication; legacy apps cannot process MFA challenges.
✓
Deploy Microsoft Entra Application Proxy with pre-authentication
Why this is correct
Application Proxy acts as a reverse proxy, handling modern auth with Entra ID and relaying to the legacy app.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→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 company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this SC-100 question in full detail.
Identify which SC-100 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Design security solutions for infrastructure — This question tests Design security solutions for infrastructure — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Deploy Microsoft Entra Application Proxy with pre-authentication — Option C is correct because Microsoft Entra Application Proxy allows publishing on-premises apps with legacy authentication, and it can integrate with Entra ID for pre-authentication, enabling SSO and MFA without code changes. Option A is wrong because Entra ID Conditional Access policies require modern authentication to enforce MFA. Option B is wrong because the Microsoft Authentication Library (MSAL) requires app code changes. Option D is wrong because federation with ADFS still requires modern auth at the app level.
What should I do if I get this SC-100 question wrong?
Identify which SC-100 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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