Docs using Sphinx

docs/extensions.rst

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+.. _extensions:
+
+Extensions
+==========
+
+Given that :ref:`provisions` and :ref:`virtual-parameters` are executed in a
+sandbox environment, it is not possible to interact with external sources or
+execute any action that requires OS, file system, or network access. Extensions
+exist to bridge that gap.
+
+Extensions are fully-privileged Node.js modules and as such have access to
+standard Node libraries and 3rd party packages. Functions exposed by the
+extension can be called from Provision scripts using the ``ext()`` function. A
+typical use case for extensions is fetching credentials from a database to have
+that pushed to the device during provisioning.
+
+By default, the extension JS code must be placed under ``config/ext``
+directory. You may need to create that directory if it doesn't already exist.
+
+The example extension below fetches data from an external REST API and returns
+that to the caller:
+
+.. literalinclude:: ext-sample.js
+  :language: javascript
+
+To call this extension from a Provision or a Virtual Parameter script:
+
+.. code:: javascript
+
+  // The arguments "arg1" and "arg2" are passed to the latlong. Though they are
+  // unused in this particular example.
+  const res = ext("ext-sample", "latlong", "arg1", "arg2");
+  log(JSON.stringify(res));