Securing Your Web App: A Developer's Checklist

Introduction

Security is a continuous process, not a single task. This checklist gives developers practical, prioritized actions to reduce risk across the full lifecycle of a web application — design, build, deploy, and operate. Use it as a living document: automate where possible, measure continuously, and iterate after incidents or audits.

High-Level Principles

• Least Privilege: Give users, services, and components only the permissions they absolutely need.
• Defense in Depth: Apply multiple, independent controls (network, app, data, infra) so a single failure doesn’t lead to compromise.
• Fail Securely: On error, default to denying access or reducing functionality rather than revealing sensitive state.
• Shift Left: Move security earlier into design and CI/CD (SAST, dependency checks, policy gates).

Design & Architecture

• Threat Modeling: Perform a lightweight threat model for major features and data flows (identify assets, trust boundaries, and likely attacker goals).
• Data Classification: Label sensitive data (PII, credentials, payment data) and apply controls accordingly (encryption, access controls).
• API & Contract Security: Define explicit API contracts (OpenAPI/GraphQL schema) and validate inputs/outputs at the edge.
• Zero Trust Principles: Treat all network calls as untrusted; authenticate and authorize every request.

Authentication & Authorization

• Use Proven Identity Systems: Prefer established identity providers or libraries (OIDC, OAuth2, SAML) rather than rolling your own.
• Multi-Factor Authentication (MFA): Enforce MFA for privileged accounts and administrative interfaces.
• Strong Session Management: Use secure, HttpOnly cookies or short-lived bearer tokens; rotate and revoke tokens as needed.
• Role-Based & Attribute-Based Access Control: Centralize authorization logic and avoid duplicating permission checks across services.

Transport & Data Protection

• HTTPS Everywhere: Enforce TLS (minimum TLS 1.2, prefer 1.3). Redirect HTTP to HTTPS and use HSTS with an appropriate max-age once stable.
• Encrypt Sensitive Data at Rest: Use strong encryption (AES-256) for databases, backups, and object storage; manage keys with a KMS.
• Protect Secrets: Store secrets in a vault (HashiCorp Vault, cloud KMS/Secret Manager), avoid checked-in secrets, and rotate creds regularly.

Input Validation & Output Encoding

• Validate Inputs: Whitelist expected types/values server-side; never trust client-side validation alone.
• Escape & Encode Outputs: Apply context-aware encoding for HTML, JavaScript, CSS, and URL contexts to prevent XSS.
• Sanitize File Uploads: Restrict file types, scan for malware, store uploads outside the webroot, and serve via signed URLs.

Security Headers & Browser Controls

Set response headers to reduce attack surface. Example minimal header set (adapt for your app):

Strict-Transport-Security: max-age=63072000; includeSubDomains; preload
Content-Security-Policy: default-src 'self'; script-src 'self' 'nonce-...'; object-src 'none'
Referrer-Policy: no-referrer-when-downgrade
X-Frame-Options: DENY
X-Content-Type-Options: nosniff
Permissions-Policy: geolocation=(), microphone=()

Use nonces or hashes for CSP script allowances and iterate CSP in report-only mode first to avoid breaking production.

Dependency & Supply Chain Security

• Lock and Pin Dependencies: Use lockfiles (package-lock.json / yarn.lock / pnpm-lock.yaml) and pin major versions where appropriate.
• Automated Scanning: Integrate SCA tools (Snyk, Dependabot, OSV) into CI to detect vulnerable libs and transitive dependencies.
• Build Reproducibility: Use reproducible builds and verify upstream artifacts (signed packages where available).
• Minimal Images & Packages: Use minimal base images and remove unnecessary packages to reduce attack surface.

Secure Coding & CI/CD

• SAST & Linting: Run static analysis in CI and address findings before merging.
• Secret Scanning: Block commits containing plaintext secrets and fail the build if detected.
• Immutable Artifacts: Produce versioned, immutable artifacts and deploy those rather than rebuilding in each environment.
• Least-Privilege CI Runners: Limit CI credentials and use ephemeral tokens. Avoid storing long-lived secrets in CI.

Runtime Protections & Infrastructure

• Network Segmentation: Isolate databases and internal services behind private networks and restrict inbound rules.
• WAF & Edge Protections: Use a Web Application Firewall and edge rules to block common attack patterns and bad bots.
• Rate Limiting & Throttling: Apply rate limits to APIs and auth endpoints to slow brute-force and abuse.
• Container & Cloud Hardening: Scan images, use read-only file systems where possible, and enforce minimal IAM policies.

Logging, Monitoring & Incident Response

• Centralized Logging: Collect logs (auth events, errors, anomalous API activity) centrally and retain according to policy.
• Alerting & SLOs: Define security SLOs (e.g., mean time to detect) and set alerts for unusual authentication patterns, privilege escalations, or spike in errors.
• RUM & EDR: Combine real-user monitoring and endpoint detection for broader visibility.
• Runbooks & Playbooks: Maintain step-by-step incident response runbooks for common scenarios (data leak, credential compromise, DDOS).
• Tabletop Exercises: Practice incident response quarterly to refine communications, containment, and recovery procedures.

Testing & Validation

• Penetration Testing: Schedule periodic pentests (internal and third-party) focused on high-risk areas.
• DAST: Run dynamic scans against staging environments with realistic data and authentication flows.
• Fuzzing & Chaos: Consider fuzzing inputs for critical services and chaos tests for resilience under failure.
• Continuous Verification: Re-run automated security tests in CI for every PR to prevent regressions.

Privacy & Compliance

• Data Minimization: Collect only necessary data and document retention policies.
• Privacy by Design: Provide clear consent UX and easy mechanisms for data access, export, and deletion.
• Compliance Mapping: Map controls to regulatory requirements you must meet (GDPR, PCI-DSS, HIPAA, etc.) and automate evidence collection where possible.

Operational Checklist (Quick Wins)

1. Enable HTTPS and HSTS across all domains.
2. Rotate secrets and enforce vault usage for production credentials.
3. Pin CSP in report-only, review reports, then enforce.
4. Enable MFA for all admin and contributor accounts.
5. Integrate dependency scanning and SAST into CI pipelines.
6. Configure centralized logging and set alerts for suspicious auth patterns.
7. Review IAM roles and remove excessive privileges.
8. Run a vulnerability scan and prioritize fixes by exploitability and impact.

Helpful Example: Simple Express.js Security Middleware

Quick example showing common headers and basic rate limiting (concept only):

const helmet = require('helmet');
const rateLimit = require('express-rate-limit');

app.use(helmet()); // Security headers
app.use(rateLimit({
windowMs: 15 * 60 * 1000,
max: 100 // tune per endpoint
}));

// Example: enforce HTTPS behind a proxy
app.use((req, res, next) => {
if (req.headers['x-forwarded-proto'] !== 'https') {
return res.redirect(301, 'https://' + req.hostname + req.originalUrl);
}
next();
}); 

Do not use this snippet as a complete solution—adapt to your auth model, deployment topology, and threat profile.

Maintaining Security as You Scale

• Security Champions: Embed security-minded engineers in product teams to keep practices practical and context-aware.
• Automate Remediation Where Safe: Auto-fix trivial issues (e.g., dependency updates) but require human review for high-risk changes.
• Measure Risk Over Time: Track mean time to remediate (MTTR) vulnerabilities, number of high-severity findings, and incident counts.

Conclusion

Securing a web application requires a combination of good architecture, strong development practices, automated tooling, and mature operations. Use this checklist to prioritize actions that reduce the biggest risks first, automate repetitive controls, and build a culture where security is part of the developer workflow. Revisit the checklist after significant product changes or incidents and keep improving.

Need help with a security review or to integrate security into your CI/CD pipeline? Check our Security & DevOps services or book a consultation.