authSource (--authenticationdatabase)

[mwjackson]

Authenticate using the authSource option when supplied

This is required when the user's authentication credentials exist on a separate DB to the one we are connecting to (a more common scenario with the new MMS)

[markunsworth]

Just to add some more detail; if you want to centralise authentication into one database you need to be able to use the source parameter of the db.authenticate method. Especially useful if you want to give a single user access to several databases on the same server.

Some reference to this:
PyMongo

mongodb