limited access allow to customer within office

Hello everyone,

My client want to allow website within office network but there is some limitation so kindly give idea how to setup this .

limitation is every agent has no Static IP so i cant white list for every agent IP.

so there is any solution to allow website only in office network or PC. I have searched some solution one is install ActiveX to agents PCs so get all information and we can block outer but network we cant. 

so any way to block all outer network and allow only office network access by code or Certification 

Thanks

Dharmesh