Validation, Authentication and Authorization

Content Overview

This article expands on a previous tutorial covering basic CRUD API creation with Express.js, focusing on crucial security aspects: validation, authentication, and authorization. We'll build upon the previous example, so familiarity with that material is recommended. The complete project is available on GitHub (link provided below).

Key Concepts

• Validation: Ensuring user-provided data conforms to predefined rules and standards. This is paramount for security, preventing vulnerabilities like SQL injection. Several resources highlight the importance of robust validation (links provided below).

• Authentication: Verifying a user's identity. This typically involves checking credentials (e.g., username/email and password) against stored records.

• Authorization: Determining what actions a user is permitted to perform. This controls access to resources based on user roles and permissions.

Implementing Validation

We'll create validation functions for name, amount, and date fields:

• name: String, non-empty, 10-255 characters.
• amount: Number or numeric string, positive, non-empty.
• date: String, optional (defaults to current date if omitted), YYYY-MM-DD format.

These functions (located in validations.js) utilize type checking and basic format validation. More comprehensive validation (e.g., date range checks) could be added.

<code class="language-javascript">// validations.js (excerpt)
const isString = (arg) => typeof arg === "string";
const isNumber = (arg) => !isNaN(Number(arg));

function isValidName(name) { /* ... */ }
function isValidAmount(amount) { /* ... */ }
function isValidDate(date) { /* ... */ }

module.exports = { isValidName, isValidAmount, isValidDate };</code>

Adding Authentication and Authorization

For demonstration, we'll use in-memory data storage (an array of objects) for users and expenses. This is not suitable for production.

The data.js file stores user and expense data:

<code class="language-javascript">// data.js (excerpt)
let users = [
    { id: "...", email: "...", password: "..." }, //Example User
    // ...more users
];

let expenditures = [
    { id: "...", userId: "...", name: "...", amount: ..., date: "..." }, //Example Expense
    // ...more expenses
];

module.exports = { expenditures, users };</code>

Signup Endpoint (/users/signup)

This endpoint creates new users. It validates email and password, checks for email duplicates, generates a UUID, and (for this demo only) stores the raw password. A base64 encoded authentication token (email:UUID) is returned. Password hashing is omitted for simplicity but is crucial in a production environment.

Login Endpoint (/users/login)

This endpoint authenticates existing users. It validates credentials and returns a base64 encoded authentication token if successful.

Protected Endpoints

To protect endpoints (e.g., /expenditures), we'll require an authentication token in the request headers (Authorization header). The token is decoded, the user is verified, and only the user's own data is returned.

<code class="language-javascript">// validations.js (excerpt)
const isString = (arg) => typeof arg === "string";
const isNumber = (arg) => !isNaN(Number(arg));

function isValidName(name) { /* ... */ }
function isValidAmount(amount) { /* ... */ }
function isValidDate(date) { /* ... */ }

module.exports = { isValidName, isValidAmount, isValidDate };</code>

Conclusion

This article provided a basic introduction to validation, authentication, and authorization in a Node.js/Express.js API. Remember that the security measures demonstrated here are simplified for educational purposes and should not be used in production systems. Production-ready applications require robust password hashing, secure token management (JWTs are recommended), and database integration.

Resources

• Source Code
• Basic CRUD API with Express
• Why Form Validation Is Important
• Input Validation: Client-side or Server-side?
• Data Validation in Your Backend
• Data Validation Best Practices
• In Defense of D
• JavaScript Essentials
• OWASP Input Validation Cheat Sheet

(Remember to replace the bracketed placeholders with actual links.)

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