+https://developers.yubico.com/Software_Projects/Yubico_OTP/YubiCloud_Validation_Servers/[host
+your own verification server].
+
+[[pveum_user_configured_totp]]
+User configured TOTP authentication
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Users can choose to enable 'TOTP' as a second factor on login via the 'TFA'
+button in the user list (unless the realm enforces 'YubiKey OTP').
+
+[thumbnail="screenshot/gui-datacenter-users-tfa.png"]
+
+After opening the 'TFA' window, the user is presented with a dialog to setup
+'TOTP' authentication. The 'Secret' field contains the key, which can simply be
+generated randomly via the 'Randomize' button. An optional 'Issuer Name' can be
+added to provide information to the 'TOTP' app what the key belongs to.
+Most 'TOTP' apps will show the issuer name together with the corresponding
+'OTP' values. The user name is also included in the QR code for the 'TOTP' app.
+
+After generating a key, a QR code will be displayed which can be used with most
+OTP apps such as FreeOTP. Now the user needs to verify both the current user
+password (unless logged in as 'root'), as well as the ability to correctly use
+the 'TOTP' key by typing the current 'OTP' value into the 'Verification Code'
+field before pressing the 'Apply' button.
+
+[[pveum_configure_u2f]]
+Server side U2F configuration
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+To allow users to use 'U2F' authentication, the server needs to have a valid
+domain with a valid https certificate. Initially an 'AppId'
+footnote:[AppId https://developers.yubico.com/U2F/App_ID.html]
+needs to be configured.
+
+NOTE: Changing the 'AppId' will render all existing 'U2F' registrations
+unusable!
+
+This is done via `/etc/pve/datacenter.cfg`, for instance:
+
+----
+u2f: appid=https://mypve.example.com:8006
+----