In a well controlled environment you typically do not want people logging into servers with privileged access (absent of additional external processes, such as a keystroke logged session manager). If you have 5 SAs all logging in as root then how can you audit activity and determine if it was Tom, Dick or Harry that rebooted the server? Similarly you don’t want DBAs directly logging in as oracle; how do you know who dropped the production table?
If your organisation is anything typical then you have multiple web sites and application that require authentication. If you’re lucky then you might have something like CA Siteminder, but your staff still complain about needing to re-authenticate every so often. The more times they need to login, the greater the chance of a mistake, causing a lockout and driving people to distraction. So you hatch a plan; let’s do a true Single Sign On.
Identity and Access Management (IAM) historically consists of the three A’s Authentication What acccount is being accessed? Authorization Is this account allowed access to this machine? Access Control What resources are you allowed to use? On top of this we may also need to consider Auditing Log the attempt to use the machine Provisioning How does the account get onto the machine?