OpenVPN with ChromeOS / ChromiumOS (ChromeBook, ChromeBit etc)
1
    Go to Client Area > Config Generator in our web site, choose ChromeOS and other options. Download files: you need user certificate "user.p12" file and Openvpn connection "

2
    Click your bottom-right panel, and then the gear to open the control panel.
    
3
    Type "certificates" in the search box and select  Manage Certificates 
    
In some version of ChromeOS the certificates menu entry is accessible only In the browser.
Open a new tab in the Chrome browser and put chrome://settings/certificates in the address bar, then press enter.

4
    On  "Your Certificates" tab, click "IMPORT AND BIND", and select the  "user.p12"  file. If asked, leave password empty. You should now see your certificate and “(hardware-backed)” if done correctly. 
    Note: if "IMPORT AND BIND" option is not available then the TPM chip is disabled or missing, please see here. Without Binding ("hardware-backed") the certificates the VPN connection cannot work.


5
    In the browser, open chrome://net-internals , and click  ChromeOS at the bottom 
6
     Choose File . Select the .onc file. It will look like it did nothing.
    
7
    Now in your bottom-right panel, you will have a VPN connection.
    
8
    Click to connect. If you forced to enter a password, type something, it doesn't matter what. Verify that in "user certificate" is selected your import certificate (hardware-backed).
    
9
    Check whether connection is ok in the bottom-right panel.
    
Many thanks to @nopcode85 for his help.
