LibreOffice is a flexible and extensible application suite. You can expand the functionality of LibreOffice with extensions available from LibreOffice Extension Center.
The LibreOffice extensions are software plug-ins that you install on top of the standard LibreOffice download, and that add some kind of additional functionality to the suite, either to one particular application (e.g. Writer, Calc or Impress) or to the whole suite.
LibreOffice has 3 kinds of extensions.
SyncOffice suite provides one extension written in Java: SyncOffice Login Extension. It's provided as libreoffice-login-extension.oxt or libreoffice-login-extension-yyyymmdd.oxt (yyyymmdd is its file creation date).
SyncOffice Login Extension source code is forked from the "LibreOffice Starter Extension" project