Moved calendar provider to its own section

Signed-off-by: Christian Wolf <github@christianwolf.email>

Author: christianlupus

developer_manual/digging_deeper/groupware/calendar.rst

@@ -104,93 +104,6 @@ The returned objects implement ``\OCP\Calendar\ICalendar``. Study the interface
 
 .. note:: All calendars are by default only readable, therefore ``ICalendar`` does not offer methods for mutation. Some of the calendars are mutable, however, and they may further extend the interface ``\OCP\Calendar\ICreateFromString``.
 
-.. _calendar-providers:
-
-Calendar providers
-------------------
-
-Nextcloud apps can register calendars in addition to the internal calendars of the Nextcloud CalDAV back end. Calendars are only loaded on demand, therefore a lazy provider mechanism is used.
-
-To provide calendar(s) you have to write a class that implements the ``ICalendarProvider`` interface.
-
-.. code-block:: php
-
-    <?php
-
-    use OCP\Calendar\ICalendarProvider;
-
-    class CalendarProvider implements ICalendarProvider {
-
-        public function getCalendars(string $principalUri, array $calendarUris = []): array {
-            $calendars = [];
-            // TODO: Run app specific logic to find calendars that belong to
-            //       $principalUri and fill $calendars
-
-            // The provider can simple return an empty array if there is not
-            // a single calendar for the principal URI
-            if (empty($calendars)) {
-                return [];
-            }
-
-            // Return instances of \OCP\Calendar\ICalendar
-            return $calendars;
-        }
-    }
-
-This ``CalendarProvider`` class is then registered in the :ref:`register method of your Application class<Bootstrapping>` with ``$context->registerCalendarProvider(CalendarProvider::class);``.
-
-
-Write support
-~~~~~~~~~~~~~
-
-Calendars that only return `ICalendar` are implicitly read-only. If your app's calendars can be written to, you may implement the ``ICreateFromString``. It will allow other apps to write calendar objects to the calendar by passing the raw iCalendar data as string.
-
-.. code-block:: php
-
-    <?php
-
-    use OCP\Calendar\ICreateFromString;
-
-    class CalendarReadWrite implements ICreateFromString {
-
-        // ... other methods from ICalendar still have to be implemented ...
-
-        public function createFromString(string $name, string $calendarData): void {
-            // Write data to your calendar representation
-        }
-
-    }
-
-Handling iMIP data 
-~~~~~~~~~~~~~~~~~~
-
-You may implement the ``IHandleIMipMessage`` interface to process iMIP data you receive in a client and want to pass on for processing to the backend. 
-
-Please be aware that there are some security considerations to take into account. You can find more infomation on these and the conditions that have to be fulfilled for iMIP data to be processed in the `RFC <https://www.rfc-editor.org/rfc/rfc6047>`_
-
-.. code-block:: php
-
-    <?php
-
-    use OCP\Calendar\IHandleIMipMessage;
-
-    class HandleIMipMessage implements IHandleIMipMessage {
-
-        public function handleIMipMessage(string $name, string $calendarData): void {
-            // Validation and write to your calendar representation
-        }
-
-    }
-
-Access through CalDAV
-~~~~~~~~~~~~~~~~~~~~~
-
-.. versionadded:: 27
-
-As with the built-in calendars, calendars provided by ``ICalendarProvider`` can be accessed using CalDAV. Therefore, permissions of the ``ICalendar`` are automatically mapped to the DAV object.
-Write support is also supported. Please note that deleting entities is currently implemented by setting the entity to the canceled state and passing it to the ``createFromString`` method.
-
-
 Resources
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