docs(developer): document app password scopes for app developers

Signed-off-by: Peter Ringelmann <peter.ringelmann@nextcloud.com>

Author: pringelmann

developer_manual/basics/controllers.rst

@@ -879,6 +879,8 @@ To turn off checks the following *Attributes* can be added before the controller
 * ``#[NoTwoFactorRequired]``: A user can access the page before the two-factor challenge has been passed (use this wisely and only in two-factor auth apps, e.g. to allow setup during login)
 * ``#[NoCSRFRequired]``: Don't check the CSRF token (use this wisely since you might create a security hole; to understand what it does see :ref:`CSRF in the security section <csrf_introduction>`)
 
+App passwords that a user limited to some parts of their account can't call any method by default, unless the user granted the whole app. To open single methods to them, see :doc:`../digging_deeper/app_password_scopes`.
+
 .. note::
 
     The attributes are only available in Nextcloud 27 or later. In older versions annotations with the same names exist:

developer_manual/digging_deeper/app_password_scopes.rst

@@ -0,0 +1,139 @@
+===================
+App password scopes
+===================
+
+.. versionadded:: 36
+
+Since Nextcloud 36, users can limit an app password to some parts of their account,
+for example only Files or only Calendar. Each part is a *scope*, a string like
+``files:files:read``. Users pick them in *Settings > Security > Devices & sessions*
+by choosing *Custom* access.
+
+A limited app password can't use your app's API or DAV collections until the user grants
+your whole app, or you add scopes to your controller methods. App passwords with full
+access and browser sessions work as before.
+
+Closed by default
+-----------------
+
+A limited app password can't reach:
+
+* Controller methods without a scope attribute. They are refused with ``403`` (over OCS
+  v1, in the OCS status of the response).
+* Pages. A ``TemplateResponse`` is refused, even if the method has a scope.
+* Admin-only methods, even when the user is an admin. A method counts as admin-only
+  when it has none of ``#[NoAdminRequired]``, ``#[SubAdminRequired]`` and ``#[PublicPage]``.
+* Your app's DAV collections, see `Opening DAV collections`_.
+
+Granting a whole app
+--------------------
+
+Your app works with a limited app password without any changes, as long as the user
+limits it to your whole app. The app password then stores your app ID, like ``deck``,
+and can use your controller methods and DAV collections, with or without
+``#[TokenScope]``. Pages and admin-only methods stay closed.
+
+Users can grant any app that is enabled for them, except apps that are reached through
+scopes, like Files, Calendar, Contacts, Tasks and Notifications.
+
+Opening controller methods
+--------------------------
+
+To open single methods instead, add ``#[TokenScope]`` to a controller class or method.
+A limited app password can then call the method if it holds that scope:
+
+.. code-block:: php
+
+    <?php
+
+    declare(strict_types=1);
+
+    namespace OCA\MyApp\Controller;
+
+    use NCU\AppFramework\Http\Attribute\TokenScope;
+    use OCP\AppFramework\Http\Attribute\NoAdminRequired;
+    use OCP\AppFramework\Http\DataResponse;
+    use OCP\AppFramework\OCSController;
+
+    #[TokenScope(scope: 'myapp:notes:write')]
+    class NotesController extends OCSController {
+        #[NoAdminRequired]
+        #[TokenScope(scope: 'myapp:notes:read')]
+        public function list(): DataResponse {
+            // Needs myapp:notes:read
+        }
+
+        #[NoAdminRequired]
+        public function create(string $text): DataResponse {
+            // Needs myapp:notes:write from the class
+        }
+    }
+
+The attribute on a method replaces the one on its class. It doesn't add to it.
+
+It's safest to put the write scope on the class and the read scope on the read
+methods. A method added later then needs the write scope until you decide otherwise.
+
+Users can't pick your own scopes in Settings yet, only your whole app. They become useful
+once clients can ask for scopes themselves.
+
+.. note::
+
+    ``TokenScope`` is in the ``NCU`` namespace, so it can still change until it moves to
+    ``OCP``. See :doc:`api`.
+
+Naming scopes
+-------------
+
+Name scopes ``<appid>:<resource>:<action>``, for example ``deck:boards:read``. The
+action is usually ``read`` or ``write``.
+
+Apps that don't ship with Nextcloud can only use scopes that start with their own app
+ID. A method that asks for another app's scope is refused for every limited app
+password, even one that holds that scope.
+
+Opening DAV collections
+-----------------------
+
+DAV collections that an app registers in its ``info.xml`` belong to that app:
+
+.. code-block:: xml
+
+    <sabre>
+        <collections>
+            <collection>OCA\MyApp\Sabre\RootCollection</collection>
+        </collections>
+    </sabre>
+
+For the example app, a limited app password needs ``myapp:dav:read`` to read them
+(``GET``, ``HEAD``, ``OPTIONS``, ``PROPFIND``, ``REPORT``, ``SEARCH``) and
+``myapp:dav:write`` for everything else, or the whole app. Users can only grant the
+whole app in Settings so far.
+
+Built-in scopes
+---------------
+
+These are the scopes users can pick in Settings. Apps that don't ship with Nextcloud
+can't ask for them, but it helps to know what an app password may hold.
+
+========================================== ==============================================
+Scope                                      Gives access to
+========================================== ==============================================
+``files:files:read``                       Reading through the Files and Sharing APIs, previews
+``files:files:write``                      Changing files. Without it, all files are read-only
+``files:dav:read``, ``files:dav:write``    Files over WebDAV
+``files_sharing:shares:write``             Creating and changing shares
+``files_trashbin:dav:read``, ``…:write``   Deleted files over WebDAV
+``files_versions:dav:read``, ``…:write``   File versions over WebDAV
+``dav:calendar:read``, ``…:write``         Calendars over CalDAV and the calendar APIs
+``dav:contacts:read``, ``…:write``         Address books over CardDAV, contacts import
+``core:search:read``                       Unified search
+``core:people:read``                       Autocomplete, contacts menu, hovercards and profile fields
+``notifications:notifications:read``       Notifications and push
+========================================== ==============================================
+
+Trying it out
+-------------
+
+Create an app password with *Custom* access in Settings, tick your app, and call your API
+with it. Untick it again to check that your app refuses the app password.

developer_manual/digging_deeper/auth.rst

@@ -11,4 +11,5 @@ Users & Authentication
    status
    out_of_office
    oidc
+   app_password_scopes
    two-factor-provider

developer_manual/release_notes/new.rst

@@ -11,6 +11,14 @@ This pages covers new features of the platform.
     Every feature should just have a brief description. Details have to be documented on a dedicated, persistent page.
     After branch-off the contents below will be cleared.
 
+App password scopes
+-------------------
+
+Users can limit an app password to some parts of their account. A limited app password
+can only use your app if the user grants the whole app, or if you open single controller
+methods with ``#[TokenScope]`` (``NCU\AppFramework\Http\Attribute\TokenScope``).
+See :doc:`../digging_deeper/app_password_scopes`.
+
 Email template blocks
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