A network access authentication system including a directory service containing a remote access password and a standard access password for each user of the network, using an authentication protocol that provides information on whether a user is accessing the network locally of remotely, and including a front-end between the directory service and the authentication protocol. The front-end executes the steps of: receiving a user identifier and a user password entered by a user through said authentication protocol; retrieving from the directory service the remote access password and the standard access password corresponding to the user identifier; if the authentication protocol indicates a remote access, comparing the user password to the remote access password, else comparing the user password to the standard access password; and granting access to the network if the comparing step is successful.