When using Azure Cognitive Services, how can you ensure that only your applications access the service?

The correct answer is to require a valid subscription key for access. In Azure Cognitive Services, the subscription key serves as a primary method of authentication. When an application requests access to a service, it must include this key in the request headers. This mechanism ensures that only applications that possess the valid key can communicate with the service, effectively controlling access.

Using a subscription key is a straightforward approach to secure Azure Cognitive Services, as it enables you to manage permissions and can be monitored or rotated to enhance security practices. This method aligns with Azure’s broader security model that emphasizes identity verification and controlled access to resources.

While limiting access to trusted networks and implementing user password authentication are valid security practices, they do not directly pertain to securing access at the service level in Azure Cognitive Services. Trusted networks may restrict access based on IP addresses but do not inherently authenticate who is making the request. User password authentication pertains more to scenarios where user logins are necessary, rather than application-level access to services. Machine learning algorithms can enhance security but do not directly impose access restrictions by themselves.