3.1. Security Best Practices for Applications

💡 First Principle: Never hard-code credentials, always use least-privilege IAM roles, and let managed services handle authentication — these three rules prevent the vast majority of security incidents.

What breaks when developers ignore security best practices? Leaked API keys in source code. Overly permissive IAM policies that give every Lambda function admin access. User authentication logic with exploitable flaws. These aren't theoretical — they're the most common security failures in AWS environments.

Think of application security like layers of an onion: IAM controls who can do what, Cognito handles user identity, Secrets Manager protects sensitive values, and Security Groups control network access. Think of it like airport security — identification (IAM), boarding pass check (Cognito), baggage screening (encryption), and terminal access control (VPC) each catch threats the others miss. What would happen if you skipped just one? Without IAM, any authenticated user could access any resource. Without Cognito, you'd build authentication from scratch — and likely introduce vulnerabilities.

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