How a Facebook Sign-Up Request Is Validated, Stored and Confirmed on the Server

Explain what Facebook's sign-up endpoint does: what the server receives, checks and produces between the moment a new person submits the registration form and the moment their account is ready to use. No knowledge of Meta's internal systems is expected. Describe how an endpoint like this works, starting from what the public sign-up form collects. ```hint Follow one request Trace a single registration request in order: what arrives, what gets checked, what gets written, what gets started in the background, and what goes back to the client. ``` ### Clarifying Questions - Should I cover the web form, the mobile apps, or both, given they likely call the same backend logic? - Does sign-up end when the account record exists, or should I include confirming the email address or phone number? - How deep should I go: the request and response contract only, or also the services and storage behind it? ### What a Strong Answer Covers - The request contract: method and transport, the fields sent, and what the client receives on success and on each kind of error - Validation and policy checks: field formats, the minimum age, and an email or phone number that is already registered - Security and integrity: how the password is stored, rate limiting, and defenses against bots and fake accounts - Side effects: the account and profile records, the confirmation message, the first session and analytics events - Product trade-offs: how each check affects sign-up conversion versus abuse, and which metrics would show it ### Follow-up Questions - Two sign-up requests with the same phone number arrive at the same instant. How does the system avoid creating two accounts? - The SMS provider in one country starts failing. What should the endpoint do, and what would you monitor? - Should the endpoint tell someone that their email address is already registered? What are the privacy and conversion trade-offs?