Assuming you want to use features inherant to "typical" Cisco network devices, . . .
If "user" can be an IP address, depending on platform and its IOS features, you can often rate-limit and/or shape.
Do keep in mind, unless you're only doing this for a few "users", it tends to be maintenance intensive, and unless you manage ingress's far side egress, you might not get the results you expect/desire.
