Best Practices for Building Secure Applications with Deno

In today’s fast-paced digital landscape, security is a top priority for developers and businesses alike. With the rise of modern runtime environments like Deno, developers are equipped with tools that prioritize security and developer experience. Deno, created by Ryan Dahl (the original creator of Node.js), was designed with security as a core principle, offering features like sandboxing, permission control, and TypeScript support out of the box.

However, no runtime can guarantee security without following best practices during development. In this blog post, we’ll explore the best practices for building secure applications with Deno, ensuring your applications are robust, reliable, and protected against vulnerabilities.

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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:

  deno run --allow-net --allow-read app.ts
  

  Avoid using the --allow-all flag unless absolutely necessary.

• Audit Permissions Regularly: Review your application’s permission requirements and remove unnecessary permissions to reduce the attack surface.

• Use Deno.permissions API: Dynamically request and revoke permissions during runtime for better control:

  const status = await Deno.permissions.request({ name: "read" });
  if (status.state === "granted") {
    console.log("Permission granted!");
  }
  

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2. Keep Dependencies Minimal and Audited

Third-party dependencies are a common source of vulnerabilities. While Deno uses a decentralized module system (no node_modules), it’s still crucial to vet the libraries you use.

Best Practices:

• Use Trusted Sources: Prefer modules hosted on deno.land/x or other reputable registries. Always verify the source code of third-party modules.

• Lock Dependencies: Use a lock.json file to ensure consistent dependency versions across environments. Generate it with:

  deno cache --lock=lock.json --lock-write app.ts
  

• Audit Dependencies: Regularly review your dependencies for known vulnerabilities. Tools like deno audit can help:

  deno audit
  

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3. Write Secure Code

Secure applications start with secure code. Deno’s TypeScript support and modern JavaScript features can help you write safer, more maintainable code.

Best Practices:

• Use TypeScript: TypeScript reduces runtime errors by enforcing type safety. Deno supports TypeScript natively, so take full advantage of it.

• Validate User Input: Always validate and sanitize user input to prevent injection attacks. Libraries like zod can help with schema validation:

  import { z } from "https://deno.land/x/zod/mod.ts";
  
  const schema = z.object({
    username: z.string(),
    password: z.string().min(8),
  });
  
  const data = schema.parse({ username: "user", password: "securepass" });
  

• Avoid Hardcoding Secrets: Use environment variables for sensitive data like API keys or database credentials. Deno provides the Deno.env API for accessing environment variables securely:

  const apiKey = Deno.env.get("API_KEY");
  

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4. Implement Secure Communication

Secure communication is essential for protecting data in transit. Deno makes it easy to implement HTTPS and secure WebSocket connections.

Best Practices:

• Use HTTPS: Always use HTTPS for web applications. Deno’s std/http module supports HTTPS natively:

  import { serve } from "https://deno.land/std/http/server.ts";
  
  const options = { certFile: "./cert.pem", keyFile: "./key.pem" };
  serve((req) => new Response("Hello, HTTPS!"), { port: 443, ...options });
  

• Secure WebSockets: Use wss:// for WebSocket connections to ensure encrypted communication.

• Enable CORS: Configure Cross-Origin Resource Sharing (CORS) policies to control which domains can access your resources. Use Deno’s std/http utilities to set CORS headers.

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5. Monitor and Handle Errors Gracefully

Error handling is a critical aspect of application security. Poor error handling can expose sensitive information or leave your application vulnerable to attacks.

Best Practices:

• Use Try-Catch Blocks: Wrap critical code in try-catch blocks to handle unexpected errors gracefully:

  try {
    const data = await fetch("https://api.example.com/data");
    const json = await data.json();
  } catch (error) {
    console.error("Error fetching data:", error);
  }
  

• Avoid Exposing Stack Traces: Never expose detailed error messages or stack traces to users. Log errors securely and return generic error messages to clients.

• Implement Logging: Use structured logging to monitor application behavior and detect anomalies. Deno’s std/log module is a great choice:

  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.debug("Debugging information");
  

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6. Regularly Update Deno and Dependencies

Staying up-to-date with the latest versions of Deno and your dependencies ensures you benefit from security patches and new features.

Best Practices:

• Update Deno: Regularly check for new Deno releases and update your runtime:

  deno upgrade
  

• Update Dependencies: Use the deno cache command to refresh your dependencies and ensure you’re using the latest versions.

• Monitor Security Advisories: Keep an eye on security advisories for Deno and your dependencies to stay informed about potential vulnerabilities.

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7. Test for Security Vulnerabilities

Testing is a crucial step in building secure applications. Incorporate security testing into your development workflow to identify and fix vulnerabilities early.

Best Practices:

• Use Static Analysis Tools: Tools like deno lint can help identify potential security issues in your code:

  deno lint
  

• Perform Penetration Testing: Simulate attacks on your application to identify weaknesses. Tools like OWASP ZAP or Burp Suite can assist with this.

• Automate Testing: Integrate security tests into your CI/CD pipeline to catch vulnerabilities before deployment.

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Conclusion

Building secure applications with Deno is easier when you follow best practices and leverage the runtime’s built-in security features. By carefully managing permissions, auditing dependencies, writing secure code, and staying up-to-date, you can significantly reduce the risk of vulnerabilities in your applications.

Deno’s modern design and focus on security make it an excellent choice for developers who prioritize safety and performance. Start implementing these best practices today to build secure, scalable, and reliable applications with Deno.

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What’s Next?
Ready to dive deeper into Deno? Check out the official Deno documentation for more tips and resources. If you have any questions or additional tips, feel free to share them in the comments below!