diff --git a/composer.json b/composer.json
index 9794196db..1c4b54347 100644
--- a/composer.json
+++ b/composer.json
@@ -431,7 +431,7 @@
 		}
 	],
 	"require": {
-		"php": ">=5.6.40",
+		"php": ">=7.0.0",
 
 		"afarkas/html5shiv": "3.7.*",
 		"alvaro-prieto/colresizable": "1.6",
@@ -492,7 +492,8 @@
 
 		"rmariuzzo/jquery-checkboxes": "1.0.7",
 
-		"sabre/dav": "1.8.10",
+		"sabre/dav": "4.0.3",
+		"sabre/event": "5.0.3",
 		"scottjehl/respond": "1.4.2",
 
 		"tapmodo/jcrop": "2.0.4",
diff --git a/webdav/Caldav_Backend.php b/webdav/Caldav_Backend.php
index bcb8edcb7..8a008f43b 100644
--- a/webdav/Caldav_Backend.php
+++ b/webdav/Caldav_Backend.php
@@ -8,6 +8,8 @@ require_once(dirname(__FILE__).'/../include/datum.class.php');
  */
 class MySabre_CalDAV_Backend extends \Sabre\CalDAV\Backend\AbstractBackend
 {
+	protected $auth;
+
     /**
      * Creates the backend
      *
@@ -54,12 +56,13 @@ class MySabre_CalDAV_Backend extends \Sabre\CalDAV\Backend\AbstractBackend
                 'uri' => 'LVPlan-'.$user,
                 'principaluri' => 'principals/'.$user,
                 '{' . \Sabre\CalDAV\Plugin::NS_CALENDARSERVER . '}getctag' => 'LVPlan-'.$user.'-'.time(),
-                '{' . \Sabre\CalDAV\Plugin::NS_CALDAV . '}supported-calendar-component-set' => new \Sabre\CalDAV\Property\SupportedCalendarComponentSet(array('VEVENT','VTODO')),
+                '{' . \Sabre\CalDAV\Plugin::NS_CALDAV . '}supported-calendar-component-set' => new \Sabre\CalDAV\Xml\Property\SupportedCalendarComponentSet(array('VEVENT','VTODO')),
 				'{DAV:}displayname'                          => 'LVPlan',
 		        '{urn:ietf:params:xml:ns:caldav}calendar-description' => 'description comes here',
 		        '{urn:ietf:params:xml:ns:caldav}calendar-timezone'    => 'Europe/Vienna',
 		        '{http://apple.com/ns/ical/}calendar-order'  => '1',
-		        '{http://apple.com/ns/ical/}calendar-color'  => '#FF0000'
+		        '{http://apple.com/ns/ical/}calendar-color'  => '#FF0000',
+		        '{http://sabredav.org/ns}read-only' => 1
         );
 		$calendars[] = $calendar;
 
@@ -117,9 +120,9 @@ class MySabre_CalDAV_Backend extends \Sabre\CalDAV\Backend\AbstractBackend
      * @param array $mutations
      * @return bool|array
      */
-    public function updateCalendar($calendarId, array $mutations)
+    public function updateCalendar($calendarId, \Sabre\DAV\PropPatch $propPatch)
 	{
-        return false;
+        $propPatch->setRemainingResultCode(403);
     }
 
     /**
@@ -213,7 +216,7 @@ class MySabre_CalDAV_Backend extends \Sabre\CalDAV\Backend\AbstractBackend
 				foreach($val as $row)
 				{
 					//einzelnen Eintrag holen
-					if($row['dtstart']==$dtstart && ($row['unr'][0]==$unr) || $unr=='R'.$row['reservierung_id'])
+					if($row['dtstart']==$dtstart && (($row['unr'][0]==$unr) || $unr=='R'.$row['reservierung_id']))
 					{
 						return $row;
 					}
@@ -251,6 +254,48 @@ TZOFFSETTO:+0100
 END:STANDARD
 END:VTIMEZONE\n".$event."\nEND:VCALENDAR";
 	}
+
+	protected function getObjectUri($row)
+	{
+		// Reservierungen werden mit einem R markiert und mit der ReservierungID da sonst
+		// Termine verloren gehen koennen wenn zur selben Zeit eine Reservierung und ein LVPlan Eintrag vorhanden ist
+		if($row['reservierung'])
+			$uri = $row['dtstart'].'-R'.$row['reservierung_id'];
+		else
+			$uri = $row['dtstart'].'-'.$row['unr'][0];
+
+		return $uri.'@'.md5($row['UID']);
+	}
+
+	protected function buildCalendarObject($row, $calendarId)
+	{
+		$calendarData = $this->makeCal($row['data']);
+
+		return array("id"=>$row['UID'],
+		"calendardata"=>$calendarData,
+		"uri"=>$this->getObjectUri($row),
+		"lastmodified"=>$this->getLastModifiedTimestamp($row['updateamum']),
+		"etag"=>'"'.$row['UID'].'"',
+		"calendarid"=>$calendarId,
+		"size"=>strlen($calendarData),
+		"component"=>'vevent');
+	}
+
+	protected function getLastModifiedTimestamp($lastModified)
+	{
+		if($lastModified === null || $lastModified === '')
+			return null;
+
+		if(is_numeric($lastModified))
+			return (int)$lastModified;
+
+		$timestamp = strtotime($lastModified);
+		if($timestamp === false)
+			return null;
+
+		return $timestamp;
+	}
+
     /**
      * Returns all calendar objects within a calendar.
      *
@@ -283,20 +328,7 @@ END:VTIMEZONE\n".$event."\nEND:VCALENDAR";
 		$return  = array();
 		foreach($data as $row)
 		{
-			// Reservierungen werden mit einem R markiert und mit der ReservierungID da sonst
-			// Termine verloren gehen koennen wenn zur selben Zeit eine Reservierung und ein LVPlan Eintrag vorhanden ist
-			if($row['reservierung'])
-				$uri = $row['dtstart'].'-R'.$row['reservierung_id'];
-			else
-				$uri = $row['dtstart'].'-'.$row['unr'][0];
-
-			$return[] = array("id"=>$row['UID'],
-			"calendardata"=>$this->makeCal($row['data']),
-			"uri"=>$uri.'@'.md5($row['UID']),
-			"lastmodified"=>$row['updateamum'],
-			"etag"=>'"'.$row['UID'].'"',
-			"calendarid"=>$calendarId);
-
+			$return[] = $this->buildCalendarObject($row, $calendarId);
 		}
 		return $return;
     }
@@ -319,23 +351,13 @@ END:VTIMEZONE\n".$event."\nEND:VCALENDAR";
 		//$user = $this->getUser();
 		$user = $calendarId;
 		$data = $this->getCalendarData($user,$objectUri);
-		if(count($data)==0)
+		if(empty($data))
 		{
-			$ret=array("id"=>'',
-			"calendardata"=>'',
-			"uri"=>'',
-			"lastmodified"=>'',
-			"etag"=>'',
-			"calendarid"=>$calendarId);
+			return null;
 		}
 		else
 		{
-			$ret = array("id"=>$data['UID'],
-			"calendardata"=>$this->makeCal($data['data']),
-			"uri"=>'principals/'.$user.'/LVPlan/'.$data['dtstart'].'-'.$data['unr'][0].'@'.md5($data['UID']),
-			"lastmodified"=>$data['updateamum'],
-			"etag"=>'"'.$data['UID'].'"',
-			"calendarid"=>$calendarId);
+			$ret = $this->buildCalendarObject($data, $calendarId);
 		}
 		return $ret;
     }
diff --git a/webdav/Principal.php b/webdav/Principal.php
index 7e3241dac..7b802ce80 100644
--- a/webdav/Principal.php
+++ b/webdav/Principal.php
@@ -32,6 +32,7 @@ class MySabre_DAVACL_PrincipalBackend implements \Sabre\DAVACL\PrincipalBackend\
     protected $groupMembersTableName;
 
 	protected $result_ma;
+	protected $auth;
     /**
      * Sets up the backend.
      *
@@ -121,16 +122,6 @@ class MySabre_DAVACL_PrincipalBackend implements \Sabre\DAVACL\PrincipalBackend\
 
 			}*/
 		}
-		else //if($prefixPath=='principals/oesi')
-		{
-			$user = mb_substr($path,11);
-		    $principals[] = array(
-					'id' => $user.'proxyread',
-		            'uri' => 'principals/'.$user.'/calendar-proxy-read',
-		            '{DAV:}displayname' => '',
-		            '{http://sabredav.org/ns}email-address' => '',
-		        );
-		}
 
         return $principals;
 
@@ -226,13 +217,18 @@ class MySabre_DAVACL_PrincipalBackend implements \Sabre\DAVACL\PrincipalBackend\
 		throw new \Sabre\DAV\Exception('Not implemented');
     }
 
-   public function updatePrincipal($path, $mutations)
+   public function updatePrincipal($path, \Sabre\DAV\PropPatch $propPatch)
    {
-	throw new \Sabre\DAV\Exception('Not implemented');
+	$propPatch->setRemainingResultCode(403);
    }
 
-	public function searchPrincipals($prefixPath,array $searchProperties)
+	public function searchPrincipals($prefixPath, array $searchProperties, $test = 'allof')
 	{
-		throw new \Sabre\DAV\Exception('Not implemented');
+		return array();
+	}
+
+	public function findByUri($uri, $principalPrefix)
+	{
+		return null;
 	}
 }
diff --git a/webdav/auth.class.php b/webdav/auth.class.php
index 00ad83415..4c9c398d7 100644
--- a/webdav/auth.class.php
+++ b/webdav/auth.class.php
@@ -25,12 +25,25 @@ require_once(dirname(__FILE__).'/../include/functions.inc.php');
 
 class myauth extends \Sabre\DAV\Auth\Backend\AbstractBasic
 {
+	protected $currentUser = null;
+
 	function validateUserPass($username, $password)
 	{
 		if(checkldapuser($username,$password))
+		{
+			$this->currentUser = $username;
 			return true;	
+		}
 		else
+		{
+			$this->currentUser = null;
 			return false;
+		}
+	}
+
+	public function getCurrentUser()
+	{
+		return $this->currentUser;
 	}
 }
 ?>
diff --git a/webdav/lvplan.php b/webdav/lvplan.php
index 684ebb1c3..57e3b265b 100644
--- a/webdav/lvplan.php
+++ b/webdav/lvplan.php
@@ -19,7 +19,7 @@ $calendarBackend = new MySabre_CalDAV_Backend($authBackend);
 
 $tree = array(
 	new \Sabre\CalDAV\Principal\Collection($principalBackend),
-	new \Sabre\CalDAV\CalendarRootNode($principalBackend, $calendarBackend)
+	new \Sabre\CalDAV\CalendarRoot($principalBackend, $calendarBackend)
 );
 
 // The object tree needs in turn to be passed to the server class
@@ -32,7 +32,8 @@ $path = str_replace($_SERVER['DOCUMENT_ROOT'],'',__FILE__).'/';
 $server->setBaseUri($path);
 
 // Authentication plugin
-$authPlugin = new \Sabre\DAV\Auth\Plugin($authBackend,'SabreDAV');
+$authBackend->setRealm('SabreDAV');
+$authPlugin = new \Sabre\DAV\Auth\Plugin($authBackend);
 $server->addPlugin($authPlugin);
 
 // CalDAV plugin