Question 264 of 928

Design and implement build and release pipelines →easyMultiple ChoiceObjective-mapped

ACR Push Authentication Error: Service Principal Lacks AcrPush Role

This AZ-400 practice question tests your understanding of design and implement build and release pipelines. 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 team uses GitHub Actions to build a Docker image and push it to Azure Container Registry (ACR). The workflow fails with the error 'unauthorized: authentication required'. The workflow uses the 'azure/docker-login@v1' action. 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.

A
The 'azure/docker-login@v1' action does not support ACR.
Why wrong: The action supports ACR.
B
The Dockerfile is not in the repository root.
Why wrong: The error is about authentication, not Dockerfile location.
C
The service principal used for authentication lacks the AcrPush role on the ACR.
AcrPush role is required to push images.
D
The workflow uses the registry admin credentials, which are disabled.
Why wrong: Admin credentials are not required with service principal.

Full breakdown with real-world context →

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

The service principal used for authentication lacks the AcrPush role on the ACR.

The 'azure/docker-login@v1' action authenticates Docker with Azure Container Registry using a service principal. If the service principal lacks the AcrPush role, Docker login succeeds but the subsequent push fails with 'unauthorized: authentication required' because the identity does not have permission to push images. The error occurs at push time, not login time, which is a key diagnostic clue.

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 'azure/docker-login@v1' action does not support ACR.
Why it's wrong here
The action supports ACR.
✗
The Dockerfile is not in the repository root.
Why it's wrong here
The error is about authentication, not Dockerfile location.
✓
The service principal used for authentication lacks the AcrPush role on the ACR.
Why this is correct
AcrPush role is required to push images.
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 workflow uses the registry admin credentials, which are disabled.
Why it's wrong here
Admin credentials are not required with service principal.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates assume the error means the login itself failed, but the 'azure/docker-login@v1' action can succeed with a valid service principal that lacks push permissions, and the 'unauthorized' error surfaces only during the subsequent docker push, leading test-takers to incorrectly suspect admin credentials or Dockerfile location.

Detailed technical explanation

How to think about this question

Under the hood, 'azure/docker-login@v1' executes 'docker login <acr-login-server> -u <client-id> -p <client-secret>', which stores credentials in Docker's config.json. The push then uses those cached credentials; if the service principal's RBAC role (e.g., AcrPush) is missing, the ACR token validation fails with HTTP 401. In real-world scenarios, this often happens when the service principal is created with only AcrPull or no role at all, and the team forgets to assign AcrPush via Azure CLI or portal.

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.

What to study next

Got this wrong? Here's your next step.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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FAQ

Questions learners often ask

What does this AZ-400 question test?

Design and implement build and release pipelines — This question tests Design and implement build and release pipelines — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: The service principal used for authentication lacks the AcrPush role on the ACR. — The 'azure/docker-login@v1' action authenticates Docker with Azure Container Registry using a service principal. If the service principal lacks the AcrPush role, Docker login succeeds but the subsequent push fails with 'unauthorized: authentication required' because the identity does not have permission to push images. The error occurs at push time, not login time, which is a key diagnostic clue.

What should I do if I get this AZ-400 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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