dynamic database connection

[eluser]Unknown[/eluser]
Hi,
I am newbie in CI, i come from .NET, and want to use CI for my new project as a web GUI.

i have several databases, and i want to users able to manage their databases.
users data stores in USERS_TABLE and database login info stores in SERVERS_TABLE.

user must able to login and have access to related database (some controllers do logics ).
in fact i want to generate dynamic database connection for user (based on related db info) in some controllers.

how i can do this ?
please suggest me some idea.

tanks all.