Quick Answer
The answer is to configure a Lambda authorizer to validate the OAuth 2.0 token. This is correct because API Gateway’s custom Lambda authorizer allows you to offload authentication logic by invoking a Lambda function that validates the token from an external identity provider (IdP) against OAuth 2.0 standards, returning an IAM policy to grant or deny access. On the AWS Certified Solutions Architect Professional SAP-C02 exam, this scenario tests your ability to distinguish between API Gateway’s authentication mechanisms, often setting traps where Cognito User Pools might seem correct but fail when the IdP is external and not Amazon Cognito. A common memory tip is to remember that “external IdP” always points to a custom Lambda authorizer, not a built-in Cognito integration. For the exam, think “external equals Lambda” to avoid the trap of selecting Cognito or misreading the requirement as needing a VPC Link or usage plan.
This SAP-C02 practice question tests your understanding of design for new solutions. 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 company is designing a new application on AWS that uses Amazon API Gateway and AWS Lambda to expose a RESTful API. The API must authenticate requests using OAuth 2.0 with an external identity provider (IdP). The company wants to offload the authentication logic to the API Gateway. Which API Gateway feature should they use?
Use API Gateway's WebSocket API.
Why wrong: WebSocket is for bidirectional streaming, not REST authentication.
Enable API Gateway's VPC Link.
Why wrong: VPC Link is for integrating with private VPC resources.
Configure a Lambda authorizer to validate the OAuth 2.0 token.
Lambda authorizer can call the IdP to validate tokens and return an IAM policy.
Use usage plans with API keys.
Why wrong: API keys are for throttling, not authentication.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Configure a Lambda authorizer to validate the OAuth 2.0 token.
Option A is correct because API Gateway supports OAuth 2.0 authorization using Cognito User Pools or custom authorizers with Lambda. Option B is wrong because WebSocket API is for real-time communication. Option C is wrong because VPC Link is for private integrations. Option D is wrong because usage plans are for API keys, not authentication.
Key principle: Authentication proves identity; authorization controls what that identity can do after login. Both must work for full privileged access.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Use API Gateway's WebSocket API.
Why it's wrong here
WebSocket is for bidirectional streaming, not REST authentication.
Enable API Gateway's VPC Link.
Why it's wrong here
VPC Link is for integrating with private VPC resources.
Configure a Lambda authorizer to validate the OAuth 2.0 token.
Why this is correct
Lambda authorizer can call the IdP to validate tokens and return an IAM policy.
Related concept
Authentication checks who the user is.
Use usage plans with API keys.
Why it's wrong here
API keys are for throttling, not authentication.
Common exam traps
Logging in proves the user can authenticate. It does not automatically mean the user is allowed to enter privileged or configuration mode. Watch for AAA authorization, privilege level and command authorization details.
Detailed technical explanation
This kind of question is testing the difference between identity and permission. A user may successfully log in to a router because authentication is working, but still fail to enter configuration mode because authorization is missing, misconfigured or mapped to a lower privilege level.
Key takeaway
Authentication proves identity; authorization controls what that identity can do after login. Both must work for full privileged access.
Real-world example
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
Review Cisco AAA concepts — authentication, authorization, and accounting. Study privilege levels (0–15), command authorization under TACACS+, and how RADIUS differs. Then practise related SAP-C02 questions on access control and AAA configuration.
Design for New Solutions — study guide chapter
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FAQ
Design for New Solutions — This question tests Design for New Solutions — Authentication checks who the user is..
The correct answer is: Configure a Lambda authorizer to validate the OAuth 2.0 token. — Option A is correct because API Gateway supports OAuth 2.0 authorization using Cognito User Pools or custom authorizers with Lambda. Option B is wrong because WebSocket API is for real-time communication. Option C is wrong because VPC Link is for private integrations. Option D is wrong because usage plans are for API keys, not authentication.
Review Cisco AAA concepts — authentication, authorization, and accounting. Study privilege levels (0–15), command authorization under TACACS+, and how RADIUS differs. Then practise related SAP-C02 questions on access control and AAA configuration.
Authentication checks who the user is.
About these practice questions
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Same concept, more angles
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 is designing a new serverless application that uses Amazon API Gateway and AWS Lambda. The application must authenticate users using a third-party identity provider (IdP) that supports OpenID Connect (OIDC). The company wants to offload authentication to the API Gateway. Which solution should the architect recommend?
mediumWhy A: Option D is correct because API Gateway can use a COGNITO_USER_POOLS authorizer with an OIDC identity provider for authentication. Option A is wrong because COGNITO_USER_POOLS supports OIDC, but Cognito must be configured as an OIDC client. Option B is wrong because Lambda authorizers are custom, not offloading authentication. Option C is wrong because IAM authorization is for AWS credentials, not OIDC.
Last reviewed: Jun 20, 2026
This SAP-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 SAP-C02 exam.
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