Most Secure Way to Give Temporary S3 Access to an External Auditor with No AWS Account
A security engineer is designing a solution to allow an external auditor to access logs in an S3 bucket in the company's AWS account. The auditor does not have an AWS account. The engineer needs to grant read-only access to the specific bucket for a limited time. Which TWO actions should the engineer take? (Choose two.)
Quick Answer
The answer is to generate a pre-signed URL for each log file and use AWS Security Token Service (STS) to issue temporary credentials. These two actions together provide the most secure way to grant temporary S3 access to an external auditor without an AWS account because they both enforce a limited time window and require no permanent identity or sign-up from the auditor. A pre-signed URL embeds credentials directly into the URL for single-object read-only access, while STS issues a temporary access key, secret key, and session token that the auditor can use to authenticate API requests to the bucket. On the AWS Certified Security Specialty SCS-C02 exam, this scenario tests your understanding of identity federation and time-bound access controls, with a common trap being to suggest creating an IAM user or sharing long-term keys. Remember the mnemonic “URL for one, STS for many” — pre-signed URLs are ideal for individual files, while STS handles broader bucket access.
⚠ Common exam trap
Test-takers frequently choose cross-account IAM roles (Option B) without realizing that the external user must have an AWS account to assume the role, which is explicitly not the case in this scenario.
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
✓
Use AWS STS to issue temporary credentials that the auditor can use to access the bucket.
AWS Security Token Service (STS) can issue temporary, limited-privilege credentials (access key, secret key, and session token) that the auditor can use to authenticate API requests to the S3 bucket. This approach does not require the auditor to have an AWS account and allows the engineer to control the validity period (via the DurationSeconds parameter) to enforce a limited time window. Option D is correct because a pre-signed URL embeds temporary credentials and a specific expiration time, granting read-only access to a single object without requiring the auditor to have AWS credentials or an AWS account.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Enable S3 Access Analyzer on the bucket to generate findings for the auditor.
Why it's wrong here
Access Analyzer only identifies potential access issues; it does not grant access.
- ✗
Create a cross-account IAM role in the company's account and share the role ARN with the auditor.
Why it's wrong here
The auditor does not have an AWS account to assume the role.
- ✓
Use AWS STS to issue temporary credentials that the auditor can use to access the bucket.
Why this is correct
STS can issue temporary credentials with a specified expiration; the auditor can use these to access the bucket.
- ✓
Generate a pre-signed URL for each log file the auditor needs to access.
Why this is correct
Pre-signed URLs provide time-limited access to specific objects without requiring AWS credentials.
- ✗
Configure the bucket policy to grant access to 'Principal': '*' with a condition that limits access to the auditor's IP address.
Why it's wrong here
This would make the bucket public; not recommended for sensitive logs.
Quick reference
AWS S3 Storage Class Comparison
| Storage Class | Min Duration | Retrieval | Use Case |
|---|---|---|---|
| S3 Standard | None | Immediate | Frequently accessed data |
| S3 Standard-IA | 30 days | Immediate | Infrequent access, rapid retrieval |
| S3 One Zone-IA | 30 days | Immediate | Non-critical infrequent data |
| S3 Intelligent-Tiering | None | Immediate–hours | Unknown or changing access patterns |
| S3 Glacier Instant | 90 days | Milliseconds | Archive with instant retrieval |
| S3 Glacier Flexible | 90 days | Minutes–hours | Archive, flexible retrieval |
| S3 Glacier Deep Archive | 180 days | Hours | Long-term compliance archive |
Go deeper
Related to this question
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Same concept, more angles
1 more way this is tested on SCS-C02
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company needs to allow an external auditor to access a specific S3 bucket for 30 days. The auditor does not have an AWS account. What is the MOST secure way to grant temporary access?
medium- A.Create an IAM user with long-term credentials and share them with the auditor.
- ✓ B.Use AWS STS to issue temporary credentials via a custom identity broker.
- C.Grant access via a bucket policy using the auditor's email address as a condition.
- D.Create an IAM role and allow the auditor to assume it using SAML federation.
Why B: The most secure method is to use AWS Security Token Service (STS) to issue temporary credentials via a custom identity broker. The broker authenticates the auditor independently (e.g., via their own corporate credentials) and then calls STS to obtain temporary, limited-privilege credentials valid for up to 36 hours. This avoids long-term credentials and does not require the auditor to have an AWS account. Option A is insecure because it exposes long-term credentials. Option C is not possible because bucket policies cannot use an email address as a condition for access without a specific IAM entity. Option D (SAML federation) requires the auditor's organization to have a SAML identity provider and a trust relationship, which may not be feasible and is less flexible than a custom broker.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This SCS-C02 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the SCS-C02 exam.