The primary security issue in this scenario is that API keys are stored in the configuration files. It is a best practice to store sensitive information such as API keys in a secure vault service rather than in configuration files.
A . Communication between the application and the services is not encrypted - Incorrect. The communication is through HTTPS, which is encrypted. B. The database credentials should be stored in the configuration files so that they are secured on the same server - Incorrect. Database credentials should be securely obtained, as mentioned, through a vault service. C. The API keys are stored in the configuration files but should be stored in the vault service - Correct. Storing API keys in configuration files poses a security risk. They should be stored in a secure vault service. D. The synchronization logs should be encrypted and not stored in a relational database - Incorrect. The issue is not about storing logs in a relational database, but rather the storage of API keys in configuration files.
Reference:
Secure Secrets Management
Best Practices for Storing API Keys