Update plugin doc

doc/plugin-authorization-architecture.markdown

@@ -0,0 +1,39 @@
+Authorization Architecture
+==========================
+
+Kanboard [supports multiple roles](roles.markdown) at the application level and at the project level.
+
+Authorization Workflow
+----------------------
+
+For each HTTP request:
+
+1. Authorize or not access to the resource based on the application access list
+2. If the resource is for a project (board, task...):
+    1. Fetch user role for this project
+    2. Grant/Denied access based on the project access map
+
+Extending access Map
+--------------------
+
+The Access List (ACL) is based on the controller class name and the method name.
+The list of access are handled by the class `Kanboard\Core\Security\AccessMap`.
+
+There are two access map: one for the application and another one for projects.
+
+- Application access map: `$this->applicationAccessMap`
+- Project access map: `$this->projectAccessMap`
+
+Example to define a new policy from your plugin:
+
+```php
+// All methods of the class MyController:
+$this->projectAccessMap->add('MyController', '*', Role::PROJECT_MANAGER);
+
+// All some methods:
+$this->projectAccessMap->add('MyOtherController', array('create', 'save'), Role::PROJECT_MEMBER);
+```
+
+Roles are defined in the class `Kanboard\Core\Security\Role`.
+
+The Authorization class (`Kanboard\Core\Security\Authorization`) will check the access for each page.