  Registration and management of users in a large scale Grid computing
environment presents new challenges that are not well addressed by existing
protocols. Within a single Virtual Organization (VO), thousands of users will
potentially need access to hundreds of computing sites, and the traditional
model where users register for local accounts at each site will present
significant scaling problems. However, computing sites must maintain control
over access to the site and site policies generally require individual local
accounts for every user. We present here a model that allows users to register
once with a VO and yet still provides all of the computing sites the
information they require with the required level of trust. We have developed
tools to allow sites to automate the management of local accounts and the
mappings between Grid identities and local accounts.
