The answer is that the SP’s metadata is missing the IdP’s certificate. This is correct because in a SAML federated identity system, the service provider must possess the identity provider’s signing certificate within its own metadata to validate the digital signature on incoming SAML assertions. Even when the IdP logs confirm the response was signed correctly, the SP cannot verify that signature without the corresponding public key, causing it to reject the authentication attempt. On the CISSP exam, this scenario tests your understanding of SAML trust establishment and the critical role metadata plays in federation—a common trap is assuming the IdP alone controls authentication success. Remember that the SP is the relying party; it must have the IdP’s certificate pre-loaded, just as a browser needs a website’s TLS certificate to trust a connection. A useful memory tip: “SP can’t sign what it doesn’t have—metadata must carry the IdP’s key to prove the claim.”
CISSP Identity and Access Management Practice Question
This CISSP practice question tests your understanding of identity and access management. 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.
An organization uses a federated identity system with SAML. A new service provider (SP) is added, but users cannot authenticate. The identity provider (IdP) logs show that the SAML response is signed correctly, but the SP rejects it. What is the most likely issue?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The SP's metadata is missing the IdP's certificate
Option E is correct because the SP must have the IdP's signing certificate in its metadata to validate the SAML response signature. If the SP's metadata is missing the IdP's certificate, the SP cannot verify the signature, causing it to reject the response even though the IdP logs show it was signed correctly.
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.
✗
The SP does not support HTTP-POST binding
Why it's wrong here
If the binding were unsupported, the IdP would likely log a different error.
✗
The IdP's clock is skewed
Why it's wrong here
Clock skew would cause the SP to reject based on time conditions, but the SP logs would show NotOnOrAfter errors.
✗
The SAML assertion is not encrypted
Why it's wrong here
Encryption is optional; signing is required but the response is signed correctly.
✗
The user's browser cookies are blocked
Why it's wrong here
Cookies are not used for SAML authentication.
✓
The SP's metadata is missing the IdP's certificate
Why this is correct
Without the IdP's certificate, the SP cannot validate the signature, so it rejects.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates confuse signature validation with encryption or assume clock skew is the default issue, but the core problem is missing trust material in the SP's metadata, not cryptographic failures or transport issues.
Trap categories for this question
Command / output trap
Clock skew would cause the SP to reject based on time conditions, but the SP logs would show NotOnOrAfter errors.
Detailed technical explanation
How to think about this question
In SAML, the SP trusts the IdP by exchanging metadata that includes certificates for signature verification. The SP's metadata must contain the IdP's signing certificate (or a trusted root) to validate the XML digital signature on the SAML response. Without this, the SP cannot establish trust, leading to rejection even if the signature is cryptographically valid. Real-world scenarios often involve misconfigured metadata exchange during SP onboarding.
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 developer is choosing between AES-256 (symmetric) and RSA-2048 (asymmetric) for encrypting a large file that will be sent to a partner. Symmetric encryption is fast but requires key exchange; asymmetric is slower but solves the key distribution problem. A hybrid approach — encrypt the file with AES, encrypt the AES key with RSA — is standard. Questions like this test whether you understand when each approach applies.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CISSP question in full detail.
Identity and Access Management — This question tests Identity and Access Management — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The SP's metadata is missing the IdP's certificate — Option E is correct because the SP must have the IdP's signing certificate in its metadata to validate the SAML response signature. If the SP's metadata is missing the IdP's certificate, the SP cannot verify the signature, causing it to reject the response even though the IdP logs show it was signed correctly.
What should I do if I get this CISSP question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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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