REST API Interview Practice Questions and Answers is my comprehensive toolkit designed to bridge the gap between basic theory and the high-level architectural knowledge required by top-tier tech companies. I’ve built this course to help you navigate the nuances of resource modeling, security protocols like OAuth 2.0, and performance optimization without the fluff. Whether you are a developer preparing for a backend role or an architect refining your design skills, I provide deep-dive explanations for every single option to ensure you understand not just the "what," but the "why" behind scalable API development. I focus heavily on real-world scenarios, covering everything from idempotency and versioning to the OWASP API Security Top 10, so you can walk into your interview or exam with the confidence of a seasoned professional.

Exam Domains & Sample Topics

• REST Fundamentals & API Design: Constraints, URI structure, and Idempotency.

• Data Handling: Content negotiation, JSON standards, and Serialization.

• API Security: JWT, OAuth 2.0, Rate Limiting, and CORS.

• Optimization: Caching strategies, Pagination, and API Gateways.

• DevOps & Testing: OpenAPI/Swagger, Postman, and Contract Testing.

Sample Practice Questions

• Which of the following HTTP methods is considered both idempotent and safe according to RFC 9110 standards?

  • A) POST

  • B) PATCH

  • C) DELETE

  • D) GET

  • E) CONNECT

  • F) TRACE

  • Correct Answer: D & F (Note: In standard MCQ, choose D as the primary answer).

  • Overall Explanation: Safety refers to methods that do not modify the resource state, while idempotency means multiple identical requests have the same effect as a single request.

  • Option Explanations:

    • A) Incorrect: POST is neither safe nor idempotent (it creates resources).

    • B) Incorrect: PATCH is not idempotent; repeated applications can change state differently.

    • C) Incorrect: DELETE is idempotent but not safe (it modifies state by removing it).

    • D) Correct: GET is safe (read-only) and idempotent.

    • E) Incorrect: CONNECT is used for tunneling and is not safe.

    • F) Correct: TRACE is safe and idempotent as it merely echoes the received request.

• When implementing an OAuth 2.0 flow for a Single Page Application (SPA) with no backend, which grant type is currently recommended by best security practices?

  • A) Implicit Grant

  • B) Resource Owner Password Credentials

  • C) Authorization Code Flow with PKCE

  • D) Client Credentials Flow

  • E) Refresh Token Flow

  • F) Device Code Flow

  • Correct Answer: C

  • Overall Explanation: Due to security vulnerabilities in the Implicit Flow, the Authorization Code Flow with Proof Key for Code Exchange (PKCE) is now the industry standard for public clients.

  • Option Explanations:

    • A) Incorrect: Implicit Grant is deprecated due to token leakage risks in the URL.

    • B) Incorrect: This requires the user to share their password directly with the app, which is insecure.

    • C) Correct: PKCE provides a cryptographically strong mechanism to prevent authorization code interception.

    • D) Incorrect: This is for machine-to-machine communication, not user-facing SPAs.

    • E) Incorrect: This is used to obtain new access tokens, not for initial authentication.

    • F) Incorrect: This is designed for input-constrained devices like Smart TVs.

• If a client requests a resource representation format that the server does not support (e.g., requesting 'application/xml' when only 'application/json' is available), which HTTP status code should I return?

  • A) 400 Bad Request

  • B) 403 Forbidden

  • C) 404 Not Found

  • D) 405 Method Not Allowed

  • E) 406 Not Acceptable

  • F) 415 Unsupported Media Type

  • Correct Answer: E

  • Overall Explanation: Content negotiation is handled via the 'Accept' header; when the server cannot fulfill this, it triggers a 406 error.

  • Option Explanations:

    • A) Incorrect: 400 is for generic client-side syntax errors.

    • B) Incorrect: 403 is for permission issues.

    • C) Incorrect: 404 means the URI itself does not exist.

    • D) Incorrect: 405 means the HTTP Verb (like PUT) isn't allowed on that URI.

    • E) Correct: 406 specifically indicates the server cannot produce a response matching the 'Accept' headers.

    • F) Incorrect: 415 is used when the client sends a payload format (Content-Type) that the server cannot process.

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