Q: You have a multi-tenant SaaS application where each client's data must be cryptographically isolated. How do you inject and manage hundreds of different database credentials dynamically without hardcoding them in config files?

Hardcoding hundreds of secrets in environment variables or configuration files is insecure and unmanageable at scale. The best practice is using a Secrets Management Engine like HashiCorp Vault. Instead of storing static passwords, you use Vault's Dynamic Secrets Engine. When the application needs to query Client A's database, it authenticates to Vault using its IAM or Kubernetes identity. Vault instantly generates a short-lived, temporary set of database credentials exclusively for Client A, hands them to the application, and automatically revokes them in the database after a set TTL (e.g., 1 hour). This eliminates the risk of long-lived leaked credentials entirely.