Which server type is commonly used for authentication and credential storage?

The directory server is specifically designed for authentication and credential storage. It provides a centralized system for managing user accounts and their associated permissions within a network. This type of server utilizes protocols such as Lightweight Directory Access Protocol (LDAP) to enable access to identity information, making it essential for managing user credentials and authentication processes efficiently.

In contrast, other server types serve different functions. A file server is primarily focused on storing and managing access to files across a network. A web server delivers web pages and content over the Internet rather than handling authentication. A DNS server's role is to translate domain names into IP addresses to facilitate network communication, not to manage user credentials or authentication processes. Therefore, the directory server stands out as the correct choice for managing authentication and credential storage within a network environment.