Best Practices for Building Secure Applications with Deno

In today’s fast-paced digital landscape, security is a top priority for developers. With the rise of modern runtime environments like Deno, building secure applications has become more streamlined and efficient. Deno, created by Ryan Dahl (the original creator of Node.js), is designed with security in mind, offering features like default sandboxing and permission control. However, no runtime is inherently foolproof, and developers must follow best practices to ensure their applications remain secure.

In this blog post, we’ll explore the best practices for building secure applications with Deno, covering everything from permission management to dependency handling. Whether you’re a seasoned developer or just starting with Deno, these tips will help you create robust and secure applications.

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1. Leverage Deno’s Built-in Security Features

One of Deno’s standout features is its secure-by-default design. Unlike Node.js, Deno does not allow access to the file system, network, or environment variables unless explicitly granted. This sandboxed approach minimizes the risk of unauthorized access or malicious code execution.

Best Practices:

• Use Permissions Wisely: Grant only the permissions your application needs. For example, if your app only requires read access to a specific file, use the --allow-read=/path/to/file flag instead of --allow-read for the entire file system.
• Audit Permissions Regularly: Review your application’s permission requirements periodically to ensure you’re not granting unnecessary access.
• Use Deno.permissions API: Dynamically request and revoke permissions at runtime using the Deno.permissions API for more granular control.

const status = await Deno.permissions.request({ name: "read", path: "./config.json" });
if (status.state === "granted") {
  console.log("Permission granted!");
} else {
  console.log("Permission denied!");
}

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2. Keep Dependencies Minimal and Secure

Third-party dependencies are a common source of vulnerabilities in any application. While Deno simplifies dependency management with its URL-based imports, it’s still crucial to vet and manage your dependencies carefully.

Best Practices:

• Pin Dependency Versions: Always specify exact versions of third-party modules in your imports to avoid unexpected updates that could introduce vulnerabilities.

import { serve } from "https://deno.land/[email protected]/http/server.ts";

• Use Trusted Sources: Stick to well-known and actively maintained modules from trusted registries like deno.land/x or the Deno standard library.
• Audit Dependencies: Regularly review your dependencies for known vulnerabilities. Tools like deno lint and deno check can help identify potential issues.

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3. Validate and Sanitize User Input

User input is one of the most common attack vectors for security breaches, including SQL injection, cross-site scripting (XSS), and command injection. Proper validation and sanitization of user input are essential to prevent these attacks.

Best Practices:

• Use Validation Libraries: Leverage libraries like zod or yup to validate and sanitize user input.
• Escape Special Characters: When working with databases or rendering HTML, ensure special characters are properly escaped to prevent injection attacks.
• Implement Strong Typing: Deno’s TypeScript support allows you to define strict types for your data, reducing the risk of unexpected input.

import { z } from "https://deno.land/x/zod/mod.ts";

const schema = z.object({
  username: z.string().min(3).max(20),
  email: z.string().email(),
});

try {
  const data = schema.parse({ username: "JohnDoe", email: "[email protected]" });
  console.log("Valid input:", data);
} catch (err) {
  console.error("Invalid input:", err.errors);
}

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4. Secure Sensitive Data

Sensitive data, such as API keys, passwords, and database credentials, must be handled with care to prevent unauthorized access.

Best Practices:

• Environment Variables: Use environment variables to store sensitive data and access them securely using Deno.env.
• Encrypt Data: Encrypt sensitive data at rest and in transit using robust encryption algorithms.
• Avoid Hardcoding Secrets: Never hardcode sensitive information directly into your codebase. Use tools like Deno’s .env support to manage environment variables securely.

import "https://deno.land/x/dotenv/load.ts";

const apiKey = Deno.env.get("API_KEY");
if (!apiKey) {
  throw new Error("API_KEY is not set in the environment variables");
}

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5. Implement Secure Communication

Secure communication is critical for protecting data in transit. Deno makes it easy to implement HTTPS and other secure protocols.

Best Practices:

• Use HTTPS: Always use HTTPS for communication between your application and external services.
• Validate Certificates: Ensure SSL/TLS certificates are valid and up-to-date.
• Enable CORS: Configure Cross-Origin Resource Sharing (CORS) policies to control which domains can access your application.

import { serve } from "https://deno.land/[email protected]/http/server.ts";

const handler = (req: Request): Response => {
  return new Response("Hello, secure world!", {
    headers: { "Content-Type": "text/plain" },
  });
};

serve(handler, { port: 8000, secure: true });

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6. Monitor and Log Application Activity

Monitoring and logging are essential for detecting and responding to security incidents. Deno provides built-in tools for logging and debugging.

Best Practices:

• Use Structured Logging: Use libraries like log to implement structured logging for better traceability.
• Monitor for Anomalies: Set up monitoring tools to detect unusual activity, such as repeated failed login attempts or unexpected permission requests.
• Protect Logs: Ensure logs do not contain sensitive information like passwords or API keys.

import { log } from "https://deno.land/std/log/mod.ts";

await log.setup({
  handlers: {
    console: new log.handlers.ConsoleHandler("DEBUG"),
  },
  loggers: {
    default: {
      level: "DEBUG",
      handlers: ["console"],
    },
  },
});

log.info("Application started successfully");

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7. Stay Updated with Deno Releases

Deno is an actively maintained runtime, and new updates often include security patches and performance improvements. Staying up-to-date with the latest version ensures your application benefits from these enhancements.

Best Practices:

• Check for Updates Regularly: Use deno upgrade to update your Deno installation to the latest version.
• Follow the Deno Blog: Keep an eye on the Deno blog for announcements about new features and security updates.

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Conclusion

Building secure applications with Deno is easier than ever, thanks to its secure-by-default design and modern features. By following these best practices—managing permissions, securing dependencies, validating input, protecting sensitive data, and staying updated—you can significantly reduce the risk of vulnerabilities in your applications.

Security is an ongoing process, and as threats evolve, so should your strategies. Start implementing these best practices today to ensure your Deno applications remain secure and reliable.

Have questions or additional tips for securing Deno applications? Share them in the comments below!