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2.2.3. Multi-Factor Authentication (MFA)

💡 First Principle: MFA requires multiple forms of identity verification, dramatically reducing the risk of compromised credentials. Even if a password is stolen, the attacker lacks the second factor.

Scenario: All users have smartphones. You need to implement MFA without additional hardware costs.

MFA Methods and Costs

MethodRequirementsAdditional Cost
Microsoft Authenticator appSmartphoneNone
SMS verificationPhone with SMSNone
Voice call verificationPhoneNone
OATH software tokensThird-party appThird-party license
OATH hardware tokensPhysical tokenToken purchase
FIDO2 security keysHardware keyKey purchase
Windows Hello for BusinessWindows deviceNone (Windows only)

⚠️ Exam Trap: Thinking all MFA methods are equal in security. SMS is vulnerable to SIM-swapping attacks. For high-security scenarios, use phishing-resistant methods like FIDO2 keys or Windows Hello for Business.

Implementing MFA

  • Per-User MFA: Legacy method, enabled per user
  • Conditional Access MFA: Recommended, policy-based approach
  • Security Defaults: Free, basic MFA for all users (good starting point)
Alvin Varughese
Written byAlvin Varughese
Founder15 professional certifications