diff --git a/docs/cpe-authentication.rst b/docs/cpe-authentication.rst
index 852934b..be32dfd 100644
--- a/docs/cpe-authentication.rst
+++ b/docs/cpe-authentication.rst
@@ -3,4 +3,70 @@
 CPE Authentication
 ==================
 
+CPE to ACS
+----------
+
+.. note::
+
+  By default GenieACS will accept any incoming connection via HTTP/HTTPS and
+  respond to it.
+
+The following paramters are used to set and get (password is redacted but
+can be set) the username/password used to authenticate against the ACS:
+
+Username: ``Device.ManagementServer.Username`` or ``InternetGatewayDevice.ManagementServer.Username``
+
+Password: ``Device.ManagementServer.Password`` or ``InternetGatewayDevice.ManagementServer.Password``
+
+Enable CPE to ACS Authentication
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+CPE to ACS authentication can be configured in the web interface by using the
+`Config` option in the `Admin` tab.
+
+Go to the `Admin` -> `Config` page and click on `New config` button at the
+bottom of the page. This will open pop-up which requires you to fill in a key
+and value. The key should be ``cwmp.auth``. The value accepts a boolean.
+Setting the value to ``true`` makes it so that GenieACS accepts any incoming
+connection, setting it to ``false`` makes GenieACS deny all incoming
+connections. This can be further configured using the ``AUTH()`` and ``EXT()``
+functions.
+
+The ``AUTH()`` function
+~~~~~~~~~~~~~~~~~~~~~~~
+
+The ``AUTH()`` function accepts two parameters, username and password. It
+checks the given username and password with the incoming request to determine
+whether to return true or false.
+
+Basic usage of the ``AUTH()`` function could be as follows:
+
+.. code:: sql
+
+   AUTH("fixed-username", "fixed-password")
+
+This will only accept incoming request who authenticate with
+"fixed-username" and "fixed-password".
+
+The various device parameters can be referenced from within the ``cwmp.auth``
+expression. For example:
+
+.. code:: sql
+
+   AUTH(Device.ManagementServer.Username, Device.ManagementServer.Password)
+
+The ``EXT()`` function
+~~~~~~~~~~~~~~~~~~~~~~
+
+The ``EXT()`` function makes it possible to call an :ref:`extension
+<extensions>` script from the auth expression. This can be used to fetch
+the credentials from an external source:
+
+.. code:: sql
+
+   AUTH(DeviceID.SerialNumber, EXT("authenticate", "getPassword", DeviceID.SerialNumber))
+
+ACS to CPE
+----------
+
 TODO