feat: add calendar delegation functionality

apps/dav/appinfo/v1/caldav.php

@@ -34,6 +34,7 @@
 use OCP\IUserManager;
 use OCP\IUserSession;
 use OCP\L10N\IFactory as IL10NFactory;
+use OCP\Mail\IMailer;
 use OCP\Security\Bruteforce\IThrottler;
 use OCP\Security\ISecureRandom;
 use OCP\Server;
@@ -58,6 +59,8 @@
 	Server::get(KnownUserService::class),
 	Server::get(IConfig::class),
 	Server::get(IL10NFactory::class),
+	Server::get(IMailer::class),
+	Server::get(LoggerInterface::class),
 	'principals/'
 );
 $db = Server::get(IDBConnection::class);

apps/dav/appinfo/v1/carddav.php

@@ -31,6 +31,7 @@
 use OCP\IUserManager;
 use OCP\IUserSession;
 use OCP\L10N\IFactory as IL10nFactory;
+use OCP\Mail\IMailer;
 use OCP\Security\Bruteforce\IThrottler;
 use OCP\Server;
 use Psr\Log\LoggerInterface;
@@ -55,6 +56,8 @@
 	Server::get(KnownUserService::class),
 	Server::get(IConfig::class),
 	Server::get(IL10nFactory::class),
+	Server::get(IMailer::class),
+	Server::get(LoggerInterface::class),
 	'principals/'
 );
 $db = Server::get(IDBConnection::class);

apps/dav/lib/CalDAV/CalendarHome.php

@@ -2,6 +2,7 @@
 
 /**
  * SPDX-FileCopyrightText: 2016-2024 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
  * SPDX-FileCopyrightText: 2016 ownCloud, Inc.
  * SPDX-License-Identifier: AGPL-3.0-only
  */
@@ -214,6 +215,36 @@ public function getChild($name) {
 		throw new NotFound('Node with name \'' . $name . '\' could not be found');
 	}
 
+	/**
+	 * @inheritdoc
+	 *
+	 * Extends the default ACL to grant proxy principals access to list this
+	 * calendar home. Individual Calendar objects already have their own proxy
+	 * ACL entries; this entry allows the PROPFIND on the home collection itself.
+	 *
+	 * @return array
+	 */
+	public function getACL(): array {
+		$acl = parent::getACL();
+		$ownerPrincipal = $this->principalInfo['uri'];
+
+		// Write-proxy delegates may list and read the calendar home so they can
+		// discover which calendars are available.
+		$acl[] = [
+			'privilege' => '{DAV:}read',
+			'principal' => $ownerPrincipal . '/calendar-proxy-write',
+			'protected' => true,
+		];
+		// Read-proxy delegates may also list the calendar home.
+		$acl[] = [
+			'privilege' => '{DAV:}read',
+			'principal' => $ownerPrincipal . '/calendar-proxy-read',
+			'protected' => true,
+		];
+
+		return $acl;
+	}
+
 	/**
 	 * @param array $filters
 	 * @param integer|null $limit

apps/dav/lib/CalDAV/Plugin.php

@@ -17,10 +17,20 @@ class Plugin extends \Sabre\CalDAV\Plugin {
 	 * This function should return null in case a principal did not have
 	 * a calendar home.
 	 *
+	 * For calendar-proxy group principals (e.g. principals/users/alice/calendar-proxy-write),
+	 * this returns the calendar home of the principal owner (alice), so that CalDAV clients
+	 * can discover and access the delegated calendar home correctly.
+	 *
 	 * @param string $principalUrl
 	 * @return string|null
 	 */
 	public function getCalendarHomeForPrincipal($principalUrl) {
+		// calendar-proxy group principals must resolve to the owner's calendar home
+		if (str_ends_with($principalUrl, '/calendar-proxy-write') || str_ends_with($principalUrl, '/calendar-proxy-read')) {
+			$ownerPrincipalUrl = substr($principalUrl, 0, strrpos($principalUrl, '/'));
+			return $this->getCalendarHomeForPrincipal($ownerPrincipalUrl);
+		}
+
 		if (strrpos($principalUrl, 'principals/users', -strlen($principalUrl)) !== false) {
 			[, $principalId] = \Sabre\Uri\split($principalUrl);
 			return self::CALENDAR_ROOT . '/' . $principalId;

apps/dav/lib/Command/CreateCalendar.php

@@ -23,6 +23,7 @@
 use OCP\IUserManager;
 use OCP\IUserSession;
 use OCP\L10N\IFactory;
+use OCP\Mail\IMailer;
 use OCP\Security\ISecureRandom;
 use OCP\Server;
 use Psr\Log\LoggerInterface;
@@ -68,6 +69,8 @@ protected function execute(InputInterface $input, OutputInterface $output): int
 			Server::get(KnownUserService::class),
 			Server::get(IConfig::class),
 			Server::get(IFactory::class),
+			Server::get(IMailer::class),
+			Server::get(LoggerInterface::class),
 		);
 		$random = Server::get(ISecureRandom::class);
 		$logger = Server::get(LoggerInterface::class);

apps/dav/lib/Connector/Sabre/Principal.php

@@ -2,6 +2,7 @@
 
 /**
  * SPDX-FileCopyrightText: 2018 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
  * SPDX-FileCopyrightText: 2016 ownCloud, Inc.
  * SPDX-License-Identifier: AGPL-3.0-only
  */
@@ -25,8 +26,10 @@
 use OCP\IUserManager;
 use OCP\IUserSession;
 use OCP\L10N\IFactory;
+use OCP\Mail\IMailer;
 use OCP\Share\IManager as IShareManager;
 use Psr\Container\ContainerExceptionInterface;
+use Psr\Log\LoggerInterface;
 use Sabre\DAV\Exception;
 use Sabre\DAV\PropPatch;
 use Sabre\DAVACL\PrincipalBackend\BackendInterface;
@@ -53,6 +56,8 @@
 		private KnownUserService $knownUserService,
 		private IConfig $config,
 		private IFactory $languageFactory,
+		private IMailer $mailer,
+		private LoggerInterface $logger,
 		string $principalPrefix = 'principals/users/',
 	) {
 		$this->principalPrefix = trim($principalPrefix, '/');
@@ -61,6 +66,7 @@
 
 	use PrincipalProxyTrait {
 		getGroupMembership as protected traitGetGroupMembership;
+		setGroupMemberSet as protected traitSetGroupMemberSet;
 	}
 
 	/**
@@ -124,6 +130,20 @@
 				if ($user !== null) {
 					return [
 						'uri' => 'principals/users/' . $user->getUID() . '/' . $name,
+						// Only the principal owner may modify their own proxy group.
+						// Any authenticated user may read it (needed by Sabre internals).
+						'{DAV:}acl' => [
+							[
+								'privilege' => '{DAV:}read',
+								'principal' => '{DAV:}authenticated',
+								'protected' => true,
+							],
+							[
+								'privilege' => '{DAV:}write',
+								'principal' => 'principals/users/' . $user->getUID(),
+								'protected' => true,
+							],
+						],
 					];
 				}
 				return null;
@@ -222,6 +242,89 @@
 		return 0;
 	}
 
+	/**
+	 * Updates the list of group members for a group principal.
+	 *
+	 * Overrides the trait implementation to send email notifications when new
+	 * write-proxy delegates are added.
+	 *
+	 * @param string $principal
+	 * @param string[] $members
+	 */
+	public function setGroupMemberSet($principal, array $members): void {
+		[$principalUri, $target] = \Sabre\Uri\split($principal);
+
+		// Snapshot the current write-proxy members before applying changes so
+		// we can diff and notify only the newly added ones.
+		$oldMemberUids = [];
+		if ($target === 'calendar-proxy-write') {
+			$oldProxies = $this->proxyMapper->getProxiesOf($principalUri);
+			foreach ($oldProxies as $proxy) {
+				if ($proxy->getPermissions() === (ProxyMapper::PERMISSION_READ | ProxyMapper::PERMISSION_WRITE)) {
+					$oldMemberUids[] = $proxy->getProxyId();
+				}
+			}
+		}
+
+		// Apply the new member set via the trait implementation.
+		$this->traitSetGroupMemberSet($principal, $members);
+
+		// Notify newly added write-proxy delegates.
+		if ($target === 'calendar-proxy-write') {
+			[, $ownerUid] = \Sabre\Uri\split($principalUri);
+			$addedMembers = array_diff($members, $oldMemberUids);
+			foreach ($addedMembers as $memberUri) {
+				[, $delegateUid] = \Sabre\Uri\split($memberUri);
+				$this->sendDelegationNotification($ownerUid, $delegateUid);
+			}
+		}
+	}
+
+	/**
+	 * Send an email to a newly added delegate informing them of the delegation.
+	 *
+	 * @param string $ownerUid  User ID of the calendar owner who granted access
+	 * @param string $delegateUid User ID of the user who was just granted access
+	 */
+	private function sendDelegationNotification(string $ownerUid, string $delegateUid): void {
+		$delegateUser = $this->userManager->get($delegateUid);
+		$ownerUser = $this->userManager->get($ownerUid);
+
+		if ($delegateUser === null || $ownerUser === null) {
+			return;
+		}
+
+		$delegateEmail = $delegateUser->getEMailAddress();
+		if ($delegateEmail === null || $delegateEmail === '') {
+			return; // No email address on file — skip silently.
+		}
+
+		$l = $this->languageFactory->get('dav');
+
+		$ownerDisplayName = $ownerUser->getDisplayName() ?: $ownerUid;
+		$delegateDisplayName = $delegateUser->getDisplayName() ?: $delegateUid;
+
+		$subject = $l->t('%s has granted you access to their calendars', [$ownerDisplayName]);
+		$bodyText = $l->t(
+			"Hello %1\$s,\n\n%2\$s has added you as a calendar delegate. You can now view and manage their\ncalendars in the Nextcloud Calendar app under the \"Delegated\" section.\n\nTo remove yourself as a delegate, ask %2\$s to revoke your access in their\nCalendar settings.",
+			[$delegateDisplayName, $ownerDisplayName]
+		);
+
+		try {
+			$message = $this->mailer->createMessage();
+			$message->setTo([$delegateEmail => $delegateDisplayName]);
+			$message->setSubject($subject);
+			$message->setPlainBody($bodyText);
+			$this->mailer->send($message);
+		} catch (\Exception $e) {
+			// Notification failure must never block the PROPPATCH response.
+			$this->logger->warning(
+				'Could not send delegation notification email',
+				['owner' => $ownerUid, 'delegate' => $delegateUid, 'error' => $e->getMessage()]
+			);
+		}
+	}
+
 	/**
 	 * Search user principals
 	 *

apps/dav/lib/Connector/Sabre/ServerFactory.php

@@ -38,6 +38,7 @@
 use OCP\IUserManager;
 use OCP\IUserSession;
 use OCP\L10N\IFactory;
+use OCP\Mail\IMailer;
 use OCP\SabrePluginEvent;
 use OCP\SystemTag\ISystemTagManager;
 use OCP\SystemTag\ISystemTagObjectMapper;
@@ -258,6 +259,8 @@ private function initRootCollection(SimpleCollection $rootCollection, Directory|
 			\OCP\Server::get(KnownUserService::class),
 			\OCP\Server::get(IConfig::class),
 			\OCP\Server::get(IFactory::class),
+			\OCP\Server::get(IMailer::class),
+			$this->logger,
 		);
 
 		// Mount the share collection at /public.php/dav/files/<share token>

apps/dav/lib/RootCollection.php

@@ -43,6 +43,7 @@
 use OCP\IUserManager;
 use OCP\IUserSession;
 use OCP\L10N\IFactory;
+use OCP\Mail\IMailer;
 use OCP\Security\ISecureRandom;
 use OCP\Server;
 use OCP\SystemTag\ISystemTagManager;
@@ -76,7 +77,9 @@ public function __construct() {
 			$proxyMapper,
 			Server::get(KnownUserService::class),
 			Server::get(IConfig::class),
-			Server::get(IFactory::class)
+			Server::get(IFactory::class),
+			Server::get(IMailer::class),
+			$logger
 		);
 
 		$groupPrincipalBackend = new GroupPrincipalBackend($groupManager, $userSession, $shareManager, $config);

apps/dav/tests/unit/CalDAV/CalendarHomeTest.php

@@ -430,4 +430,38 @@ public function testGetChildrenFederatedCalendars(): void {
 		$this->assertInstanceOf(FederatedCalendar::class, $actual[3]);
 		$this->assertInstanceOf(FederatedCalendar::class, $actual[4]);
 	}
+
+	public function testGetAclContainsProxyWritePrincipal(): void {
+		$acl = $this->calendarHome->getACL();
+
+		$principals = array_column($acl, 'principal');
+		$this->assertContains('user-principal-123/calendar-proxy-write', $principals);
+
+		// Find the specific entry and verify all fields
+		foreach ($acl as $entry) {
+			if ($entry['principal'] === 'user-principal-123/calendar-proxy-write') {
+				$this->assertSame('{DAV:}read', $entry['privilege']);
+				$this->assertTrue($entry['protected']);
+				return;
+			}
+		}
+		$this->fail('ACL entry for calendar-proxy-write not found');
+	}
+
+	public function testGetAclContainsProxyReadPrincipal(): void {
+		$acl = $this->calendarHome->getACL();
+
+		$principals = array_column($acl, 'principal');
+		$this->assertContains('user-principal-123/calendar-proxy-read', $principals);
+
+		// Find the specific entry and verify all fields
+		foreach ($acl as $entry) {
+			if ($entry['principal'] === 'user-principal-123/calendar-proxy-read') {
+				$this->assertSame('{DAV:}read', $entry['privilege']);
+				$this->assertTrue($entry['protected']);
+				return;
+			}
+		}
+		$this->fail('ACL entry for calendar-proxy-read not found');
+	}
 }

apps/dav/tests/unit/CalDAV/PluginTest.php

@@ -33,6 +33,17 @@ public static function linkProvider(): array {
 				'principals/calendar-rooms/Room-ABC',
 				'system-calendars/calendar-rooms/Room-ABC',
 			],
+			// calendar-proxy-write and calendar-proxy-read group principals must
+			// resolve to the owner's calendar home so that delegates can discover
+			// the delegated calendar home via PROPFIND on the proxy group principal.
+			[
+				'principals/users/alice/calendar-proxy-write',
+				'calendars/alice',
+			],
+			[
+				'principals/users/alice/calendar-proxy-read',
+				'calendars/alice',
+			],
 		];
 	}