cephfs mount with secretfile

When using the secretfile option for cephfs mounts:

mount -t ceph <source> /mnt -o name=myuser,secretfile=/etc/ceph/secret.key,noatime,_netdev

The following error is returned

mount: /mnt: wrong fs type, bad option, bad superblock on <source>, missing codepage or helper program, or other error.

dmesg shows:

libceph: bad option at 'secretfile=/etc/ceph/secret.key'

I already installed ceph-base. Mounting with mount.ceph directly works without problems.

(from redmine: issue id 10351, created on 2019-04-26)