The name of this strategy is phased installation. Phased installation (or phased implementation) occurs when an existing system is replaced by a new one. However, unlike most implementations, this takes place in stages. This has several advantages. First, it allows you to test the system. If there is a problem with it, it is easier to revert back to the old strategy. Moreover, if employees need to adopt this new system, it allows them to get used to it slowly while still being able to access the previous one.
In multiple enterprises there are number of authentication processes to access resources and information so in order to avoid a large number of authentications we have a process called federation whereby all the authentication and authorization processes are passes from one system to the other within the enterprise.
