Comment 9 for bug 1986593

A quick and dirty workaround is to set a bare string by hand after removing the relation. e.g.

From:
====
# ceph config dump | grep 'dashboard.*KEY'
mgr advanced mgr/dashboard/RGW_API_ACCESS_KEY {'juju-5e2cd5-0-lxd-2': '8OHNPOQMYY1FEUGAQZL2', 'juju-5e2cd5-1-lxd-3': '8OHNPOQMYY1FEUGAQZL2', 'juju-5e2cd5-2-lxd-2': '8OHNPOQMYY1FEUGAQZL2'} *
mgr advanced mgr/dashboard/RGW_API_SECRET_KEY {'juju-5e2cd5-0-lxd-2': 'I8Gb46kpqCmdBdsCNEx5bhOuEwnOGEtIb73rOK8T', 'juju-5e2cd5-1-lxd-3': 'I8Gb46kpqCmdBdsCNEx5bhOuEwnOGEtIb73rOK8T', 'juju-5e2cd5-2-lxd-2': 'I8Gb46kpqCmdBdsCNEx5bhOuEwnOGEtIb73rOK8T'} *
====

To:
ceph config set mgr mgr/dashboard/RGW_API_ACCESS_KEY 8OHNPOQMYY1FEUGAQZL2
ceph config set mgr mgr/dashboard/RGW_API_SECRET_KEY I8Gb46kpqCmdBdsCNEx5bhOuEwnOGEtIb73rOK8T

Because access_key/secret_key are common across 3 units. I'm not sure until when the manual change is persistent though since some Juju hooks will override it at some point.