How can I create a key for localhost or private IP?

All webSDK license keys work on localhost independently of the particular domain name for which the license was created. 

Additionally, all private IP ranges are supported as listed here:

https://en.wikipedia.org/wiki/Private_network

In other words, any webSDK license key should work both on the specified domain as well as on localhost. 

In case there is a problem with license validation, the logs will show a license error indicating the exact cause of the issue.