'What is the value of the strongest encryption algorithm, if users create passwords from their spouse's or pet's name, and write them on post-it memo's?'
Said Bruce Schneier, one of the world's famous cryptographers. A very weak link in access control is the user himself, being allowed to make up his own fixed passwords. Using an authentication server and the corresponding tokens allow your organization to drastically increase the level of access security.
A token is a one-time password generator based on a 3DES or AES key. The corresponding authentication server compares the user generated code to a code that was centrally generated using the same secret key. Most banks in The Netherlands, such as Rabobank and ING use this technology for their online banking environment.
Authentication servers are able to use RADIUS protocol, and thus communicate with all (remote) access systems supporting RADIUS, such as SSL and IPsec VPN systems and web servers.