React Login Series - Auth API Designing & Managing Endpoints | Part 4b

Login Feature Series: Designing & Managing Authentication API Endpoints

In the previous post of this Login Feature Series, we focused on a technical discussion on decoupling the api from authContext API decoupling into its own files.

A clean login feature isn’t just about forms and validation—it’s about predictable, secure, and well-scoped API endpoints that your frontend can trust.

This post walks through:

• The core authentication endpoints you need
• What each endpoint is responsible for
• How to structure and manage them as a feature (not a mess of routes)
• How this API aligns with the UI we’ve already built
• Philosophy: Feature-Based APIs (Not Random Endpoints)

Just like we structured our frontend as a Login Feature, the API should follow the same principle.

Instead of:

/login
/register
/reset
/change-password

We think in terms of:

/auth/*

This keeps ownership clear, improves security reasoning, and makes the feature portable.

Core Authentication Endpoint Map

Here’s the minimum complete set of endpoints needed for a modern login system:

1. POST /auth/login
2. POST /auth/logout
3. POST /auth/register
4. GET /auth/me
5. POST /auth/refresh
6. POST /auth/forgot-password
7. POST /auth/reset-password
8. PATCH /auth/update-password

Each endpoint has one responsibility—no overlap, no hidden logic.

1. POST /auth/login

Purpose:Authenticates a user using credentials (email + password).

Responsibilities

• Validate credentials
• Reject invalid logins
• Issue tokens (access + refresh)
• Return user-safe profile data

Example Response Shape

{
  "user": {
    "id": "123",
    "email": "user@example.com",
    "name": "Crystal"
  },
  "accessToken": "...",
  "refreshToken": "..."
}

Important Rule: Never return sensitive fields (password hash, internal flags).

2. POST /auth/logout

Purpose: Ends the user session.

Responsibilities

• Invalidate refresh token (server-side)
• Clear cookies if used
• Return success state

This endpoint is simple—but critical for security.

3. POST /auth/register

Purpose: Creates a new user account.

Responsibilities

• Validate input (email format, password rules)
• Enforce uniqueness
• Hash password
• Create user record
• (Optionally) auto-login after success

Your frontend password rules already exist—this endpoint must enforce the same rules.

4. GET /auth/me

Purpose: Returns the currently authenticated user.

Responsibilities

• Verify access token
• Return user profile
• Act as a session truth source

This endpoint powers:

• Route guards
• Page refresh persistence

Auto-login flows

If /auth/me fails → user is logged out.

5. POST /auth/refresh

Purpose: Issues a new access token.

Responsibilities

• Validate refresh token
• Rotate tokens (best practice)
• Return new access token

Your frontend should never guess auth state—it asks the API.

6. POST /auth/forgot-password

Purpose: Starts the password reset flow.

Responsibilities

• Accept email
• Generate reset token
• Send email (or mock it in dev)
• Always return success (prevent user enumeration)

Example safe response:

{ "message": "If an account exists, an email has been sent." }

7. POST /auth/reset-password

Purpose: Completes password reset using a token.

Responsibilities

• Validate reset token
• Validate new password
• Update password securely
• Invalidate token

This connects directly to your Confirm Reset Password UI.

8. PATCH /auth/update-password

Purpose: Changes password for logged-in users.

Responsibilities

• Require authentication
• Validate current password
• Validate new password
• Update securely

This endpoint is different from reset—and should stay separate.

API ↔ UI Mapping (Why This Matters)

Your frontend already reflects this structure:

This 1:1 mapping keeps your app predictable and debuggable.

Error Handling Strategy

All auth endpoints should follow a consistent error shape:

{
  "error": "Invalid credentials",
  "code": "AUTH_INVALID"
}

Why?

• Frontend can map errors to UI
• Guards can respond correctly
• Logs stay meaningful

Security Rules (Non-Negotiable)

• Never expose internal IDs unnecessarily
• Never confirm whether an email exists
• Always hash passwords
• Always validate input server-side
• Rotate refresh tokens
• Expire reset tokens
• Your UI is helpful.
• Your API is authoritative.

Mental Model Of Express.js setup

UI → useAuth → AuthContext → Storage
                     ↓
                  authApi

• useAuth talks to Context
• Context owns session state
• API + Storage are implementation details

Diagram: Auth Context as the App Authority

flowchart TD
  UI --> useAuth
  useAuth --> AuthContext

  AuthContext -->|login| authApi
  authApi -->|response| AuthContext

  AuthContext -->|state| UI

Final Thought

A login system isn’t “done” when the form works. It’s done when every endpoint has a clear job, a clear contract, and a clear owner. The endpoints are Backend-Agnostic Contracts and can be used to integrate in-house backends or third-party services. Backend language only matters when you cross the auth api boundary. This API design gives your Login Feature a backbone you can scale, test, and reuse.

Whats Next

Our next post in the Login Series API Code discusses break down of express api code setup, structuring the api depending on in-house development or black box endpoints, which architectural needs and prepare our system to add coding the api.