The answer is to use IAM roles on the target service and call it with the appropriate identity token from the metadata server. This is the best practice for Cloud Run service-to-service authentication because the metadata server provides a short-lived identity token that proves the caller’s service account identity, while the target Cloud Run service uses IAM roles to grant or deny invocation permission—ensuring least-privilege access without exposing long-lived secrets. On the Google Professional Cloud Developer exam, this concept tests your understanding of workload identity federation and the principle that internal microservices should never rely on API keys or OAuth2 client credentials, which are designed for external clients. A common trap is choosing the default compute service account, which often has overly broad permissions and violates the security principle of least privilege. Memory tip: think “Metadata token + IAM = internal handshake,” avoiding external keys or broad default accounts.
PCD Integrating Google Cloud services Practice Question
This PCD practice question tests your understanding of integrating google cloud services. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 developer is building a microservices application on Cloud Run. One service needs to make authenticated HTTP requests to another Cloud Run service in the same project. What is the best practice for authentication?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Why wrong: API keys are for external clients and not secure for service-to-service.
B
Use Cloud Run's built-in service-to-service authentication with the default compute service account
Why wrong: The default compute service account may have overly broad permissions; it's better to use a dedicated service account.
C
Use OAuth2 client credentials
Why wrong: OAuth2 client credentials are for external applications, not internal service-to-service.
D
Use IAM roles on the target service and call it with the appropriate identity token from the metadata server
This is the recommended approach: use a service account with the roles/run.invoker role on the target service and obtain an identity token from the metadata server.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use IAM roles on the target service and call it with the appropriate identity token from the metadata server
Option D is correct because Cloud Run service-to-service authentication is best done using an identity token from the metadata server and setting IAM on the target service. Option A is not recommended as API keys are for external clients. Option B uses OAuth2 client credentials which are for external applications. Option C uses the default compute service account which may have broader permissions than needed.
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.
✗
Use API keys
Why it's wrong here
API keys are for external clients and not secure for service-to-service.
✗
Use Cloud Run's built-in service-to-service authentication with the default compute service account
Why it's wrong here
The default compute service account may have overly broad permissions; it's better to use a dedicated service account.
✗
Use OAuth2 client credentials
Why it's wrong here
OAuth2 client credentials are for external applications, not internal service-to-service.
✓
Use IAM roles on the target service and call it with the appropriate identity token from the metadata server
Why this is correct
This is the recommended approach: use a service account with the roles/run.invoker role on the target service and obtain an identity token from the metadata server.
Clue confirmation
The clue word "best" 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
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→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 PCD exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Integrating Google Cloud services — This question tests Integrating Google Cloud services — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use IAM roles on the target service and call it with the appropriate identity token from the metadata server — Option D is correct because Cloud Run service-to-service authentication is best done using an identity token from the metadata server and setting IAM on the target service. Option A is not recommended as API keys are for external clients. Option B uses OAuth2 client credentials which are for external applications. Option C uses the default compute service account which may have broader permissions than needed.
What should I do if I get this PCD question wrong?
Identify which PCD exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Are there clue words in this question I should notice?
Yes — watch for: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
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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