To protect secrets such as API URLs, shared keys, and other application configurations, it is best practice to: C. Ensure they never appear in plaintext at rest or in transit. Encrypt sensitive data both when it is stored (at rest) and when it is transmitted over the network (in transit). This prevents unauthorized access and exposure. E. Always store secrets in a secure vault. Use dedicated secret management tools like HashiCorp Vault, AWS Secrets Manager, or Azure Key Vault to store and manage sensitive information securely. These tools provide mechanisms for access control, audit logging, and automatic rotation of secrets.