The answer is FIDO2 security keys, along with Certificate-based Authentication (CBA) and Windows Hello for Business, as these three methods enforce phishing-resistant authentication for SAML SaaS apps. FIDO2 and WebAuthn are phishing-resistant because they bind credentials to a specific web origin using public-key cryptography, meaning the private key never leaves the device and cannot be reused on a fake site, even if a user is tricked into clicking a malicious link. On the Microsoft Cybersecurity Architect exam, this question tests your ability to distinguish between true phishing-resistant methods and weaker MFA like SMS or TOTP, which are vulnerable to relay attacks. A common trap is assuming any SAML-compatible MFA is phishing-resistant, but only methods that cryptographically verify the relying party’s origin qualify. Memory tip: think “origin-bound” for FIDO2, CBA, and Windows Hello—if the authentication method doesn’t prove the real site’s identity, it’s not phishing-resistant.
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. 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.
Your company is designing a secure access strategy for a SaaS application that supports SAML 2.0. You need to enforce phishing-resistant authentication. Which THREE of the following methods meet the requirement?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
FIDO2 security keys
FIDO2 security keys (Option B) are phishing-resistant because they use public-key cryptography and are bound to a specific web origin, preventing credential reuse on fake sites. The WebAuthn protocol ensures the private key never leaves the device, and the hardware key provides strong multi-factor authentication that cannot be intercepted or relayed.
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.
✗
Microsoft Authenticator push notifications
Why it's wrong here
Push notifications can be approved without verifying intent, making them susceptible to MFA fatigue attacks.
✓
FIDO2 security keys
Why this is correct
Phishing-resistant hardware-based authentication.
Related concept
Read the scenario before looking for a memorised answer.
✓
Passkeys (FIDO2) stored on user devices
Why this is correct
Device-bound passkeys are phishing-resistant.
Related concept
Read the scenario before looking for a memorised answer.
✓
Certificate-based authentication (CBA)
Why this is correct
CBA using smart cards or certificates is phishing-resistant.
Related concept
Read the scenario before looking for a memorised answer.
✗
SMS one-time passcode (OTP)
Why it's wrong here
SMS is not phishing-resistant; can be intercepted or spoofed.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse 'multi-factor' with 'phishing-resistant,' assuming any second factor (like push notifications or SMS) is sufficient, but only FIDO2, passkeys, and certificate-based authentication meet the strict definition of phishing resistance per NIST AAL3.
Detailed technical explanation
How to think about this question
FIDO2/WebAuthn uses the CTAP2 protocol over USB, NFC, or BLE to generate a key pair per relying party; the private key is stored in secure hardware (e.g., TPM or secure element). During authentication, the browser sends a challenge signed by the private key, and the origin is verified via the RP ID, making it immune to man-in-the-middle attacks even if DNS is compromised. Certificate-based authentication (CBA) is also phishing-resistant because the client certificate is bound to the user's device and validated by the server via TLS mutual authentication, but it requires a PKI infrastructure and certificate enrollment.
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: FIDO2 security keys — FIDO2 security keys (Option B) are phishing-resistant because they use public-key cryptography and are bound to a specific web origin, preventing credential reuse on fake sites. The WebAuthn protocol ensures the private key never leaves the device, and the hardware key provides strong multi-factor authentication that cannot be intercepted or relayed.
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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Question Discussion
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