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Speak·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
Jul 2026

Summary

Speak had me design an in-memory HTTP API for user auth and profile management, basically an MVP from scratch with no real database involved. The scope felt reasonable but there were a lot of moving parts to juggle at once.

Questions Asked (2)

Q1

Design an in-memory HTTP API that supports user registration, login, profile retrieval and update, and account deletion. Walk through your data models, request/response schemas, and how you'd handle validation and errors.

System DesignAPI & IntegrationsData Modeling
Author's notes

This was a lot to cover in one shot.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the scope and constraints, then define the data models and API endpoints with clear request/response schemas. Walk through validation and error handling systematically, covering edge cases and security considerations.

Pro tip: Emphasize idempotency and security best practices like password hashing and token-based authentication, even in an in-memory design, to show production awareness.

1. Clarify Requirements and Constraints

Ask about expected scale, persistence requirements, authentication mechanisms, and any specific compliance needs. Confirm that in-memory means data is not persisted across restarts.

2. Design Data Models

Define User model with fields like id, username, email, passwordHash, createdAt, updatedAt. Consider using UUIDs for IDs and storing passwords securely with hashing.

3. Define API Endpoints and Schemas

Outline endpoints: POST /register, POST /login, GET /users/{id}, PATCH /users/{id}, DELETE /users/{id}. Specify request/response JSON schemas, including status codes and error formats.

4. Detail Validation and Error Handling

Describe input validation (e.g., email format, password strength), authentication checks, and error responses (400, 401, 404, 409). Mention consistent error structure and logging.

5. Discuss Trade-offs and Extensions

Acknowledge limitations of in-memory storage (e.g., no persistence, scalability) and suggest how to extend to a database or add features like rate limiting.

Key Points to Mention

  • Use of UUIDs for user IDs to avoid collisions and enumeration attacks.
  • Password hashing with salt (e.g., bcrypt) and never storing plaintext passwords.
  • Token-based authentication (e.g., JWT) for stateless sessions, with proper expiration and refresh mechanisms.
  • Idempotent operations for registration and updates to handle retries safely.
  • Consistent error response format with error codes and messages for client handling.
  • Consideration of concurrency and thread-safety in in-memory data structures.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.

Q2

What are the trade-offs in your current MVP design, and how would you extend it to support sessions or tokens, password resets, and audit logging?

Technical Trade-offsSystem DesignAPI & Integrations
Author's notes

The extension part is where I actually felt more confident.

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AI HintsAI Generated

Suggested Approach

Start by briefly describing your current MVP design and its trade-offs, then systematically outline how you would extend it to support sessions/tokens, password resets, and audit logging. Emphasize the balance between simplicity, security, and scalability at each step, and conclude by summarizing the key trade-offs in the extended design.

Pro tip: Acknowledge that MVP trade-offs are intentional and tie each extension to a concrete user or business need, showing you prioritize based on impact and effort. Also, mention that you would validate the design with threat modeling and incremental testing to catch issues early.

1. Describe Current MVP Design and Trade-offs

Briefly outline your MVP architecture (e.g., monolithic, simple auth) and explicitly state the trade-offs you made, such as speed vs. security or simplicity vs. scalability.

2. Extend for Sessions or Tokens

Explain how you would add session management or token-based auth (e.g., JWT, OAuth), discussing trade-offs like statelessness vs. revocation, and storage considerations.

3. Implement Password Resets

Describe a secure password reset flow (e.g., email with time-limited token), covering trade-offs like user experience vs. security and how to prevent abuse.

4. Add Audit Logging

Outline an audit logging system that captures key events (e.g., logins, password changes), discussing trade-offs like performance overhead, storage costs, and privacy.

5. Summarize and Prioritize

Summarize the extended design, reiterate the trade-offs, and explain how you would prioritize these features based on business needs and technical constraints.

Key Points to Mention

  • Stateless vs. stateful authentication (JWT vs. sessions) and their implications for scalability and revocation.
  • Security best practices for password resets: token expiration, single-use tokens, rate limiting, and secure transmission.
  • Audit logging considerations: what to log, log integrity, retention policies, and compliance (e.g., GDPR).
  • Trade-offs between development speed and long-term maintainability when extending an MVP.
  • The importance of incremental delivery and testing (e.g., A/B testing, canary releases) when adding features.
  • Potential integration points with existing systems (e.g., identity providers, logging services) and their impact on design.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.