/usr/lib/x86_64-linux-gnu/libonline-accounts-plugin.so is in libonline-accounts-plugin-dev 0.7+16.04.20160322-0ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libonline-accounts-plugin.so.1.0.0