From time to time, I see users posting on the VMTN forums with some questions and confusion around the proper implementation and functionality of vMA's vi-fastpass. The confusion is further enhanced with the new Active Directory functionality and integration with vMA's new vi-fastpass type called adauth.
The vi-fastpass component found in vMA is a credentials caching mechanism to allow you to connect to your ESX(i) or vCenter servers. Prior to vMA 4.1, vMA 4.0 only supported one type of vi-fastpass which is just called fpauth (fastpass authentication). This fpauth basically allows you to manage an ESX(i) or vCenter server under vMA by creating a vi-adminXX and vi-userXX account. The password for these two accounts are obfuscated using a simple XOR cipher. A user can now initialize one of these managed targets and execute either vCLI or vSphere SDK for Perl scripts without having to specify credentials each and every time, this works because the vi-adminXX credentials are being used to connect to your target. This can make running a simple command across n-number of hosts simple without having to provide the credentials for every host.