The control flow module is an official GeoServer extension. Installation, as usual, is quite easy. You may find the package listed among the other extension downloads on the GeoServer download page (http://geoserver.org/download/). In order to avoid compatibility issues, please ensure that you download a version of the extension exactly matching the GeoServer version you are using.
Download the ZIP archive. Please verify that the version number in the filename is the same as the GeoServer WAR file you installed. For the 2.5.2 release, the link is as follows:
Stop your GeoServer instance and then extract the contents of the ZIP archive into...