Add new post to blog about private engines

docs/blog/index.rst

@@ -8,3 +8,4 @@ Blog
    python3
    admin
    intro-offline
+   private-engines

docs/blog/private-engines.rst

@@ -0,0 +1,63 @@
+==================================
+Limit access to your searx engines
+==================================
+
+Administrators might find themselves wanting to limit access to some of the
+enabled engines on their instances. It might be because they do not want to
+expose some private information through an offline engine. Or they
+would rather share engines only with their trusted friends or colleagues.
+
+Private engines
+===============
+
+To solve this issue private engines were introduced in :pull:`1823`.
+A new option was added to engines named `tokens`. It expects a list
+of strings. If the user making a request presents one of the tokens
+of an engine, he/she is able to access information about the engine
+and make search requests.
+
+Example configuration to restrict access to the Arch Linux Wiki engine:
+
+.. code:: yaml
+
+  - name : arch linux wiki
+    engine : archlinux
+    shortcut : al
+    tokens : [ 'my-secret-token' ]
+
+
+Unless a user has configured the right token, the engine is going
+to be hidden from him/her. It is not going to be included in the 
+list of engines on the Preferences page and in the output of
+`/config` REST API call.
+
+Tokens can be added to one's configuration on the Preferences page
+under "Engine tokens". The input expects a comma separated list of
+strings.
+
+The distribution of the tokens from the administrator to the users
+is not carved in stone. As providing access to such engines
+implies that the admin knows and trusts the user, we do not see
+necessary to come up with a strict process. Instead,
+we would like to add guidelines to the documentation of the feature.
+ 
+Next steps
+==========
+
+Now that searx has support for both offline engines and private engines,
+it is possible to add concrete engines which benefit from these features.
+For example engines which search on the local host running the instance.
+Be it searching your file system or querying a private database. Be creative
+and come up with new solutions which fit your use case.
+
+Acknowledgement
+===============
+
+This development was sponsored by `Search and Discovery Fund`_ of `NLnet Foundation`_ .
+
+.. _Search and Discovery Fund: https://nlnet.nl/discovery
+.. _NLnet Foundation: https://nlnet.nl/
+
+
+| Happy hacking.
+| kvch // 2020.02.28 22:26