The answer is to enable authentication policies in Microsoft Entra ID to block legacy authentication, as this directly ensures all user authentication requests are evaluated by Conditional Access policies before granting access to cloud apps. Legacy protocols like POP3, IMAP, and SMTP with basic authentication bypass modern authentication and Conditional Access entirely, so blocking them forces clients to use modern protocols such as OAuth 2.0 or OpenID Connect, which are subject to policy evaluation. On the Microsoft Cybersecurity Architect exam, this scenario tests your understanding of how legacy authentication undermines Conditional Access enforcement—a common trap is suggesting a migration or app replacement instead of the immediate blocking control. Remember the key insight: if it doesn’t support modern auth, it can’t be governed by Conditional Access. A useful memory tip is “Block the bypass, enforce the policy”—legacy auth is the back door that must be locked first.
SC-100 Practice Question: Design solutions that align with security best practices and priorities
This SC-100 practice question tests your understanding of design solutions that align with security best practices and priorities. 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.
Your organization has a hybrid identity environment with Microsoft Entra ID and on-premises Active Directory. You need to design a solution that ensures all user authentication requests are evaluated by Conditional Access policies before granting access to cloud apps. However, some legacy apps still require basic authentication. What 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
✓
Enable authentication policies in Microsoft Entra ID to block legacy authentication
Option A is correct because enabling authentication policies in Microsoft Entra ID to block legacy authentication ensures that all user authentication requests are evaluated by Conditional Access policies before granting access to cloud apps. Legacy authentication protocols (e.g., POP3, IMAP, SMTP, basic auth) bypass modern authentication and Conditional Access, so blocking them forces clients to use modern protocols (OAuth 2.0, OpenID Connect) that are subject to Conditional Access evaluation. This directly addresses the requirement while allowing legacy apps to be updated or replaced over time.
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.
✓
Enable authentication policies in Microsoft Entra ID to block legacy authentication
Why this is correct
Blocking legacy authentication ensures all requests use modern auth, which is required for Conditional Access evaluation.
Related concept
Read the scenario before looking for a memorised answer.
✗
Configure Active Directory Federation Services (AD FS) as the identity provider
Why it's wrong here
AD FS can enforce some policies but legacy authentication may still bypass Conditional Access.
✗
Deploy Microsoft Entra Application Proxy for all legacy apps
Why it's wrong here
Application Proxy provides secure remote access but does not block legacy authentication.
✗
Enable pass-through authentication (PTA) to forward authentication requests
Why it's wrong here
PTA still allows legacy authentication protocols that bypass Conditional Access.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse 'blocking legacy authentication' with 'disabling basic authentication' in Exchange Online or other services, but the correct approach is to use the tenant-wide Conditional Access policy to block all legacy authentication protocols, which is a distinct setting in Microsoft Entra ID.
Detailed technical explanation
How to think about this question
Legacy authentication protocols (e.g., POP3, IMAP4, SMTP, and older Exchange ActiveSync) use basic authentication, which sends credentials in plaintext and does not support MFA or Conditional Access. Microsoft Entra ID Conditional Access policies evaluate only modern authentication requests (OAuth 2.0, OpenID Connect, SAML, WS-Federation). Blocking legacy authentication at the tenant level via the 'Block legacy authentication' policy in Entra ID effectively forces all clients to use modern protocols, ensuring that every authentication request is evaluated by Conditional Access. In a hybrid environment, this also requires that on-premises apps are updated to support modern authentication or are proxied through Entra Application Proxy with pre-authentication.
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 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.
Design solutions that align with security best practices and priorities — This question tests Design solutions that align with security best practices and priorities — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Enable authentication policies in Microsoft Entra ID to block legacy authentication — Option A is correct because enabling authentication policies in Microsoft Entra ID to block legacy authentication ensures that all user authentication requests are evaluated by Conditional Access policies before granting access to cloud apps. Legacy authentication protocols (e.g., POP3, IMAP, SMTP, basic auth) bypass modern authentication and Conditional Access, so blocking them forces clients to use modern protocols (OAuth 2.0, OpenID Connect) that are subject to Conditional Access evaluation. This directly addresses the requirement while allowing legacy apps to be updated or replaced over time.
What should I do if I get this SC-100 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.
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