Add ability to restrict login based on client IP

[shelby-moore]

This is a feature request for something similar to how you can restrict login/token usage by specifying a CIDR range when creating a user in the userpass backend (https://www.vaultproject.io/api/auth/userpass/index.html#bound_cidrs). Ideally I would like to restrict login using the kubernetes auth method to IPs belonging to my kubernetes cluster.

[rumenvasilev]

I believe this has been added with #67
https://www.vaultproject.io/api/auth/kubernetes/index.html#token_bound_cidrs

[jefferai]

Correct, it was added in #67, I just didn't know about this issue. Thanks for the pointer!