In the Workforce plugin (version 1.1.0) it is possible to create user accounts which will be able to access client zone. Section for clients is available under /client-zone URI. This is hardcoded URI which can be changed by translating client-zone string. You can use for that for example Say What plugin.
Creating user access to client zone
- Create regular WordPress User in admin under Users menu item
- Assign company to user in user profile
- Assign role Client to user