The answer is that the request's Origin header does not match the allowed origin. This is the most likely cause because Azure Blob Storage performs exact string matching when validating CORS requests; the browser sends an Origin header of https://www.contoso.com, and if that exact value is not listed in the storage account's CORS rules, the PUT request is blocked. On the Microsoft Azure Developer Associate AZ-204 exam, this scenario tests your understanding that CORS configuration is case-sensitive and requires precise protocol, domain, and port matching—a common trap is assuming wildcards or partial matches are accepted. Remember that Azure Blob Storage does not support wildcard origins in CORS rules; each origin must be explicitly listed. For the exam, a helpful memory tip is "CORS is a corset: it must fit exactly, no stretching allowed."
AZ-204 Develop for Azure storage Practice Question
This AZ-204 practice question tests your understanding of develop for azure storage. 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.
Refer to the exhibit. You are analyzing the Azure Blob Storage service properties configured for a storage account. A web application hosted at https://www.contoso.com attempts to make a PUT request to a blob. The request fails with a CORS error. What is the most likely cause?
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 request's Origin header does not match the allowed origin.
The CORS error occurs because the request's Origin header (https://www.contoso.com) does not match any allowed origin in the CORS rule. Azure Blob Storage enforces exact string matching for the Origin header against the allowed origins list; a mismatch causes the browser to block the PUT request. Since the question states the request fails with a CORS error and the exhibit shows allowed origins that do not include https://www.contoso.com, this is the most likely cause.
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 request includes a header that is not in the allowed headers list.
Why it's wrong here
The allowedHeaders is set to '*', so any header is allowed.
✓
The request's Origin header does not match the allowed origin.
Why this is correct
CORS requires the Origin header to match an allowed origin.
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.
✗
The CORS rule does not include the DELETE method.
Why it's wrong here
PUT is in allowedMethods, so DELETE is irrelevant.
✗
The exposedHeaders list does not include a required response header.
Why it's wrong here
ExposedHeaders are for the browser to access, not for the request.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume CORS errors are always caused by missing methods or headers, but the most common cause is a mismatch between the request's Origin header and the allowed origins list, especially when the allowed origins are not configured to include the exact domain of the web application.
Detailed technical explanation
How to think about this question
CORS in Azure Blob Storage is evaluated per request by comparing the Origin header against the allowed origins list using exact string matching (no wildcard support for subdomains unless using '*'). For PUT requests with no custom headers, the browser skips the preflight OPTIONS request and directly sends the PUT; if the Origin is not allowed, the browser blocks the response based on the missing Access-Control-Allow-Origin header. This behavior is defined by the W3C CORS specification and is critical for web applications hosted on different domains.
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 media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this AZ-204 question in full detail.
Develop for Azure storage — This question tests Develop for Azure storage — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The request's Origin header does not match the allowed origin. — The CORS error occurs because the request's Origin header (https://www.contoso.com) does not match any allowed origin in the CORS rule. Azure Blob Storage enforces exact string matching for the Origin header against the allowed origins list; a mismatch causes the browser to block the PUT request. Since the question states the request fails with a CORS error and the exhibit shows allowed origins that do not include https://www.contoso.com, this is the most likely cause.
What should I do if I get this AZ-204 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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