Added README

deps/rabbitmq_auth_backend_cache/README.md

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+# Overview
+
+This plugin provides ability to cache authentication and authorization backend
+responses to configurable amount of time.
+It's not an independent auth backend, but proxy for existing backends.
+
+This plugin will cache all requests to upstream auth backend for specific 
+(configurable) amount of time. This makes few sense if used with broker 
+internal auth backend but can be useful in LDAP, HTTP or other backends that use
+network for access checks.
+
+**Be aware that this implementation does not provide any automatical invalidation other than TTL**
+
+As with all authentication plugins, this one requires rabbitmq-server
+2.3.1 or later.
+
+## Building
+
+You can build and install it like any other plugin (see
+[the plugin development guide](http://www.rabbitmq.com/plugin-development.html)).
+
+## Enabling the Plugin
+
+To enable the plugin, set the value of the `auth_backends` configuration item
+for the `rabbit` application to include `rabbit_auth_backend_cache`.
+`auth_backends` is a list of authentication providers to try in order.
+
+
+So a configuration fragment that enables this plugin *only* would look like:
+
+    [{rabbit, [{auth_backends, [rabbit_auth_backend_cache]}]}].
+
+To configure upstream auth backend, you should use `cached_backend` configuration item
+for the `rabbitmq_auth_backend_cache` application.
+
+Configuration to use LDAP auth backend:
+
+    [{rabbitmq_auth_backend_cache, [{cached_backend, rabbit_auth_backend_ldap}]}].
+
+You can use different backends for authorization and authentication same way,
+[as it used in broker](https://www.rabbitmq.com/access-control.html):
+
+The following example configures plugin to use LDAP backend for authentication
+but internal backend for authorisation:
+
+    [{rabbitmq_auth_backend_cache, [{cached_backend, {rabbit_auth_backend_ldap,
+                                                      rabbit_auth_backend_internal}}]}].
+
+## Configuring the plugin
+
+You can configure TTL for cache items, by using `cache_ttl` configuration item, specified in **milliseconds**
+
+    [{rabbitmq_auth_backend_cache, [{cached_backend, rabbit_auth_backend_ldap}
+                                    {cache_ttl, 5000}]}].
+
+You can also use a custom cache module to store cached requests. This module
+should be an erlang module implementing `rabbit_auth_cache` behaviour.
+
+This repository contains three such modules:
+
+- `rabbit_auth_cache_dict` stores cache in internal process dictionary **this module is for demonstration only and should not be used in production**
+- `rabbit_auth_cache_ets` stores cache in `ets` table and uses timers to invalidate **this is default module**
+- `rabbit_auth_cache_ets_segmented` stores cache in multiple `ets` tables and do not deletes individual cache items, deletes tables during garbage collection periodically.
+
+
+To specify module for caching you should use `cache_module` configuration item and 
+specify start args with `cache_module_args`.
+
+    [{rabbitmq_auth_backend_cache, [{cache_module, rabbit_auth_backend_ets_segmented},
+                                    {cache_module_args, [10000]}]}].
+
+Default values is `rabbit_auth_cache_ets` and `[]` respectively.
+
+
+