title: Why CalendarProvider doesn't allow writing ExtendedProperties?
body: <p>Google calendar events have extended properties that can be used to attach name/value pairs to an event. </p>
  
  <p>We are implementing a collaborative calendar application that uses those extended properties to  attach extra information to the event. As recommended by Google, we use the Android CalendarProvider to read and create new events. When we create a new event we need to add some extended properties to it but we just realised that the calendar provider doesn't allow writing <code>CalendarContract.ExtendedProperties</code>, if we try we get the following error: </p>
  
  <p><code>Only sync adapters may write using content://com.android.calendar/extendedproperties</code></p>
  
  <p>It seems a bit weird that these properties are read-only in the CalendarProvider because it defeats the whole purpose of them that is being able to attach some extra metadata to the event. </p>
  
  <p>Does anyone know a workaround for this limitation? </p>