What protocol is often used for remote server connection authentication?

The most commonly used protocol for remote server connection authentication is RADIUS (Remote Authentication Dial-In User Service). RADIUS is primarily employed for authenticating users who are connecting to a network. It acts as a central authentication service, allowing users to log in from various locations, enabling a secure method of verifying user credentials.

RADIUS is crucial in scenarios where an organization needs to control access to its network and provides a way to manage user profiles, access rights, and accounting. It operates on the client-server model, where the client sends a request to the RADIUS server for authentication and the server returns a response indicating whether the authentication was successful.

In contrast, other choices like SSH (Secure Shell) are often implemented for secure remote connections, but it primarily focuses on encrypting data in transit rather than managing user authentication in a centralized way. While protocols like POP3 and HTTP are designed for specific purposes such as email retrieval and web traffic, respectively, they do not serve the role of remote server connection authentication nor provide secure user authentication functionalities like RADIUS does.