External authentication is the use of third-party authentication sources to decide whether a user should be allowed access to a system, and often what level of access an authenticated user enjoys on a system.
External authentication sources typically provide username information and password authentication. Other types of authentication available include client certificates (particularly with AD or LDAP servers), PINs from hardware tokens (common with RADIUS servers) or soft/browser tokens (common with SSO technology).
External authentication sources often provide file transfer servers with the full name, email address and other contact information related to an authenticating user. They can also provide group membership, home folder, address book and access privileges. When external authentication technology involves particularly rich user or partner profiles and allows users and partners to maintain their own information, then the external authentication technology used to onboard users and partners is often called “Community Management” technology.