Add document on using YubiKey with U2F (#416)

* Add document on using YubiKey with U2F

* Add yubikey doc to tutorials TOC

source/clear-linux/tutorials/tutorials.rst

@@ -32,4 +32,5 @@ Explore our tutorials to discover what you can do with |CL|!
    kubernetes/kubernetes*
    greengrass
    dlrs
+   yubikey-u2f
    nvidia

source/clear-linux/tutorials/yubikey-u2f.rst

@@ -0,0 +1,126 @@
+.. _yubikey-u2f:
+
+Enable YubiKey U2F Support 
+##########################
+
+YubiKey\* is a USB security token manufactured by `Yubico`_. Depending on the
+model, a YubiKey can support different authentication protocols including:
+One-Time Password (OTP), Smart card, FIDO2, and Universal 2nd Factor (U2F).
+
+These instructions will go over configuring a YubiKey for U2F authentication
+through a web browser on a |CL-ATTR| system. 
+
+A list of `websites
+accepting U2F authentication with the YubiKey`_ is available on the Yubico
+website. See the Yubico website to learn more about the Yubikey:
+https://www.yubico.com/getstarted/meet-the-yubikey/ 
+
+
+
+.. contents:: :local:
+   :depth: 1
+
+
+
+Prerequisites 
+*************
+
+This tutorial assumes you have: 
+
+#. |CL| installed and running.
+
+#. Mozilla Firefox installed on |CL|. 
+
+#. A YubiKey.
+
+
+
+Enable Linux udev rules for YubiKey 
+***********************************
+
+:command:`udev` is the Linux device manager which handles events when USB
+devices are added and removed. Custom rules needs to be created to properly
+identify the YubiKey and provide applications access.
+
+These instructions are derived from: `Yubico support article Using Your U2F
+YubiKey with Linux
+<https://support.yubico.com/support/solutions/articles/15000006449>`_
+
+
+#. Create the udev rules folder under :file:`/etc`
+   
+   .. code:: bash
+      
+      sudo mkdir -p /etc/udev/rules.d/
+
+
+#. Download the u2f rules from the Yubico GitHub:
+
+   .. code:: bash
+      
+      curl -O https://raw.githubusercontent.com/Yubico/libu2f-host/master/70-u2f.rules
+
+      
+#. Move the downloaded :file:`70-u2f.rules` file into the :file:`/etc/udev`
+   folder
+
+   .. code:: bash
+      
+      sudo mv 70-u2f.rules /etc/udev/rules.d/
+
+
+#. The udev rules should automatically be reloaded. However, they can be
+   manually reloaded or reboot the system:
+
+   .. code:: bash
+      
+      sudo udevadm control --reload-rules && udevadm trigger
+
+
+#. Plugin and validate the YubiKey appears as a USB device:
+
+   .. code:: bash
+      
+      lsusb
+
+
+
+Enable U2F in Mozilla Firefox 
+*****************************
+
+Firefox comes with U2F web authentication support disabled by default. U2F
+needs to be enabled in the advanced settings.
+
+These instructions are derived from: `Yubico support article Enabling U2F
+support in Mozilla Firefox
+<https://support.yubico.com/support/solutions/articles/15000017511-enabling-u2f-support-in-mozilla-firefox>`_
+
+
+#. Launch Mozilla Firefox
+
+#. In the URL bar, type :command:`about:config` to access the advanced
+   settings.
+
+   .. code:: bash
+      
+      about:config
+
+#. Click the *I accept the risk!* button to continue to the advanced settings
+
+#. Search for the :command:`security.webauth.u2f` and double-click it 
+   so *Value* becomes **true**.
+
+
+Your YubiKey is now usable on |CL| with Mozilla Firefox with websites that
+support U2F authentication.
+
+
+Related topics 
+**************
+
+- |CL| :ref:`security`
+
+
+.. _`Yubico`: https://www.yubico.com/
+
+.. _`websites accepting U2F authentication with the YubiKey`: https://www.yubico.com/works-with-yubikey/catalog/#protocol=universal-2nd-factor-(u2f)&usecase=all&key=all