User authentication mechanism for several applications installed on the same Websphere Application Server

hi experts,

I have 4 different applications installed on WAS 4.0.5. All these applications has their own db (db2) storing staff details and login access (username and password) of respective system. This created problem to us as staff details were inconsistant and users need to remember 4 sets of username and password. There is a plan to centralize staff details and login access, which means staff details will be stored at one place only and users can use the same username and password to access all these 4 systems. What is the best way to implement this? Please advise and thanks in advance!