Quick Answer
The answer is Active Directory Federation Services (AD FS). AD FS is the correct component because it acts as the bridge between on-premises Active Directory and a SAML 2.0 identity provider, translating Kerberos or NTLM authentication from AD into SAML assertions that the SaaS application can trust. In the context of the CompTIA SecurityX CAS-004 exam, this question tests your understanding of federated identity architectures and the specific role of AD FS as a Security Token Service (STS) that enables single sign-on without exposing on-premises credentials to the cloud. A common trap is confusing AD FS with a proxy like Web Application Proxy or with Azure AD; remember that AD FS is the on-premises SAML IdP, while Azure AD is the cloud-based alternative. A useful memory tip: think of AD FS as the “SAML translator” for Active Directory—it takes AD’s native tokens and repackages them into SAML for external apps.
This CAS-004 practice question tests your understanding of security engineering. 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.
A small business uses an on-premises Active Directory for user authentication. They want to enable employees to use their corporate credentials to access a SaaS application that supports SAML 2.0. The security administrator needs to set up a federation between the on-premises AD and the SaaS provider. Which of the following components must be deployed on-premises to act as a bridge between AD and the SAML identity provider?
RADIUS server
Why wrong: RADIUS is for network access, not SAML federation.
Active Directory Federation Services (AD FS)
AD FS is a SAML 2.0 IdP that authenticates against AD.
Kerberos key distribution center (KDC)
Why wrong: KDC issues Kerberos tickets, not SAML assertions.
Azure AD Connect
Why wrong: Azure AD Connect syncs to cloud, but doesn't provide SAML IdP functionality on-prem only.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Active Directory Federation Services (AD FS)
Active Directory Federation Services (AD FS) is Microsoft's solution for federated identity and can act as the SAML IdP, integrating with AD.
Key principle: Authentication proves identity; authorization controls what that identity can do after login. Both must work for full privileged access.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
RADIUS server
Why it's wrong here
RADIUS is for network access, not SAML federation.
Active Directory Federation Services (AD FS)
Why this is correct
AD FS is a SAML 2.0 IdP that authenticates against AD.
Related concept
Authentication checks who the user is.
Kerberos key distribution center (KDC)
Why it's wrong here
KDC issues Kerberos tickets, not SAML assertions.
Azure AD Connect
Why it's wrong here
Azure AD Connect syncs to cloud, but doesn't provide SAML IdP functionality on-prem only.
Common exam traps
Logging in proves the user can authenticate. It does not automatically mean the user is allowed to enter privileged or configuration mode. Watch for AAA authorization, privilege level and command authorization details.
Detailed technical explanation
This kind of question is testing the difference between identity and permission. A user may successfully log in to a router because authentication is working, but still fail to enter configuration mode because authorization is missing, misconfigured or mapped to a lower privilege level.
Key takeaway
Authentication proves identity; authorization controls what that identity can do after login. Both must work for full privileged access.
Real-world example
A junior network technician can log in to a core router but cannot reach the enable prompt or configuration mode. The AAA server is authenticating the login — but the authorisation policy only grants privilege level 1, not 15. Authentication (who you are) is working; authorisation (what you can do) is not.
What to study next
Review Cisco AAA concepts — authentication, authorization, and accounting. Study privilege levels (0–15), command authorization under TACACS+, and how RADIUS differs. Then practise related CAS-004 questions on access control and AAA configuration.
Security Engineering — study guide chapter
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FAQ
Security Engineering — This question tests Security Engineering — Authentication checks who the user is..
The correct answer is: Active Directory Federation Services (AD FS) — Active Directory Federation Services (AD FS) is Microsoft's solution for federated identity and can act as the SAML IdP, integrating with AD.
Review Cisco AAA concepts — authentication, authorization, and accounting. Study privilege levels (0–15), command authorization under TACACS+, and how RADIUS differs. Then practise related CAS-004 questions on access control and AAA configuration.
Authentication checks who the user is.
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Last reviewed: Jun 24, 2026
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