sudo apt-get install keepass2 git-coreWhere to put KeePass plugins is non-obvious, but fortunately some Googling reveals it to be at /usr/lib/keepass/plugins. Lets go there and create a directory for KeePassHTTP.
cd /usr/lib/keepass2/Great, now we just need to download the plugin. As I alluded to at the beginning we can grab the plugin via git for easier updating. The project is maintained at https://github.com/pfn/keepasshttp, but we can just grab the one plugin file we need. In fact, if we checkout the entire repository then KeePass will throw some errors as the plugin is there twice in two different formats and it can only load the plugin one time.
sudo mkdir plugins
sudo git clone -n https://github.com/pfn/keepasshttp.git --depth 1Now you can update the plugin at any time by running the following from the /usr/lib/keepass/plugins/keepasshttp directory.
sudo git checkout HEAD KeePassHttp.plgx
git pullIf you are only interested in downloading the file once and not worrying about updates you can simply download the extension file.
wget https://raw.github.com/pfn/keepasshttp/master/KeePassHttp.plgxNow you can restart KeePass2 and the plugin will be loaded.