There’s a moment every developer knows: that 2 AM alert, the spike in your monitoring dashboard, the cold realisation that something’s wrong. I’ve been there more times than I’d like to admit across seven years of building applications in healthcare, fintech, and e-commerce. Each time taught me something money can’t buy: security isn’t a feature you bolt on. It’s a mindset you build with.
Now, with Artificial Intelligence (AI) reshaping how we write, deploy, and even think about software, that mindset matters more than ever.
The Stakes Have Changed
Early in my career, I worked on a payment gateway processing tens of thousands of pounds daily. The weight of that responsibility hit me the first time I saw a real transaction fail—not because of a bug, but because our fraud detection wasn’t sophisticated enough to spot a pattern that seemed obvious in hindsight.
Later, building healthcare dashboards that delivered critical patient alerts, the stakes became even more personal. A delayed notification isn’t just a poor user experience. It’s a patient who might not get the care they need in time. When you’re aiming for 99.8% reliability on clinical alerts, you start to understand that security and reliability are two sides of the same coin.
Today, AI adds new dimensions to these challenges. We’re integrating machine learning models that make decisions we can’t always explain. We’re using AI-powered coding assistants that might inadvertently introduce vulnerabilities. We’re building systems that process data at scales our predecessors never imagined.
What I’ve Learned the Hard Way That You Should Know too
1. Authentication Is Where Trust Begins (and Often Breaks)
I’ve implemented authentication flows for mobile apps, admin portals, and everything in between. Here’s what experience has taught me: the fanciest security architecture means nothing if your authentication is weak.
In one project, we built a real-time payment monitoring system. We got the WebSocket connections working beautifully—sub-second updates, elegant UI, the works. Then during a security review, we discovered our token refresh logic had a race condition that could, in rare circumstances, leave sessions dangling. It took us two weeks to fix properly.
The lesson? Test your auth flows like they’re the most important code you’ll ever write. Because they are.
2. Real-Time Systems Demand Real-Time Thinking About Security
When you’re building systems that process thousands of daily transactions or serve tens of thousands of concurrent users, security can’t be an afterthought that slows things down. It has to be woven into the architecture from day one.
I once worked on a marketplace platform where we needed sub-200ms response times while also validating every request. The temptation to skip validation steps “just for performance” was real. We resisted it by investing in smarter validation—caching user permissions, using efficient data structures, designing our GraphQL resolvers to validate as they parsed.
The result? We hit our performance targets and our security requirements. It just took more thought upfront.
3. Compliance Isn’t Just Paperwork
Working on HIPAA-compliant healthcare systems changed how I think about compliance frameworks. At first, I saw regulations as boxes to tick. Over time, I came to see them as hard-won wisdom from people who’d seen systems fail in ways I hadn’t imagined yet.
AML checks in fintech, HIPAA in healthcare, GDPR everywhere—these frameworks exist because someone, somewhere, got hurt when systems weren’t built carefully enough. When I implemented identification and anti- money-laundering checks for a payment platform, I stopped thinking of them as bureaucratic hurdles and started thinking of them as protection for real people.
4. Your Team Is Your First Line of Defence
I’ve mentored junior developers across multiple teams, and I’ve noticed something consistent: security vulnerabilities often come from knowledge gaps, not carelessness. A developer who doesn’t understand SQL injection won’t spot it in a code review. A team that’s never discussed XSS won’t catch it in their React components.
The most secure codebases I’ve worked on weren’t just technically sound—they had cultures where asking “but is this secure?” was welcomed, not dismissed. Where code reviews included security as a first-class concern. Where we celebrated catching vulnerabilities before production, not just shipping features quickly.
The AI Factor: New Tools, New Threats, Same Principles
AI is transforming how we build software. I’ve used AI-powered recommendation engines that increased order values by 45%. I’ve seen machine learning models process patterns no human could spot manually. The potential is extraordinary.
But here’s what I keep coming back to: AI doesn’t change the fundamentals. It amplifies them.
AI-assisted coding can introduce vulnerabilities faster than any human could type them. When you’re using Copilot or similar tools, you’re not just reviewing your own code anymore—you’re reviewing suggestions from a model trained on the entire internet, including its bad security practices.
AI-powered attacks are becoming more sophisticated. Phishing emails generated by language models, deepfakes that bypass identity verification, automated vulnerability scanning at scale. The attackers have AI too.
AI decision-making creates new security surfaces. When a machine learning model decides whether to approve a transaction or flag a patient alert, how do you audit that? How do you ensure it’s not being gamed? How do you maintain explainability when regulators come asking?
My approach: treat AI as a powerful but untrusted collaborator. Verify its outputs. Constrain its permissions. Build systems that can explain their decisions. Never let automation replace human judgment on security- critical paths.
Practical Wisdom from the Trenches
If I could go back and tell my younger self a few things about building secure applications, here’s what I’d say:
Invest in observability. The payment monitoring dashboards and healthcare alerting systems I’ve built all shared one thing: you can’t secure what you can’t see. Real-time visibility into your systems isn’t a luxury. It’s a necessity.
Design for failure. That 99.9% uptime I’ve helped achieve? It came from assuming everything would break and building accordingly. Circuit breakers. Graceful degradation. Retry logic with exponential backoff. The question isn’t if something will fail, but when—and whether you’ve designed for it.
Automate the right things. Those CI/CD pipelines I’ve built that cut deployment times by 60%? They included security scanning from day one. Automated dependency checks. Static analysis. Container scanning. If it can be automated, it should be—so humans can focus on the judgment calls that can’t.
Make security convenient. Every time you make secure behaviour harder than insecure behaviour, you’re fighting human nature. The most secure systems I’ve built made doing the right thing the easy thing. Good defaults. Clear error messages. Friction in the right places, not everywhere.
The Crucial Human Element
At the end of the day, security is about people. The patient waiting for a critical alert. The family whose savings flow through your payment system. The user who trusted your platform with their data.
I think about them when I’m reviewing code at 11 PM. When I’m pushing back on a deadline because the security testing isn’t complete. When I’m mentoring a junior developer and they ask why we can’t just skip the input validation “this once.”
Technology changes. Frameworks come and go. AI will reshape our industry in ways we can’t fully predict. But the responsibility to build systems that protect the people who use them? That’s timeless.
Seven years in, I’m still learning. Still finding new ways to mess up, and hopefully, new ways to do better. The only constant is that the moment you think you’ve got security figured out is the moment you’ve become dangerous.
Stay humble. Stay curious. And never stop asking: “What could go wrong?”
About the writer: Joseph Ajayi is a Senior Software Engineer with over seven years of experience building healthcare, fintech, and e-commerce applications. He’s passionate about security, performance optimisation, and mentoring the next generation of developers.
