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 "
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2
Click your bottom-right panel, and then the gear to open the control panel.
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3
Type "certificates" in the search box and select Manage Certificates
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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.
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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.
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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.
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7
Now in your bottom-right panel, you will have a VPN connection.
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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).
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9
Check whether connection is ok in the bottom-right panel.
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Many thanks to @nopcode85 for his help.