A developer is asked to implementa simple call to an authentication - protected REST web...

The valid configuration to implement a call to an authentication-protected REST web service is to add the authentication password to the service credentials (Option A). This approach ensures that the credentials required for authentication are securely stored and utilized in the service configuration. Typically, credentials for external services should be configured within the service framework in Salesforce B2C Commerce, which allows for secure storage and usage of sensitive information such as passwords, thereby maintaining security best practices.