cassandra.yaml:
authenticator: org.apache.cassandra.auth.SimpleAuthenticator
authority: org.apache.cassandra.auth.SimpleAuthority

access.properties:
# some comments
DynamicKeyspace.<rw>=writer,root
DynamicKeyspace.<ro>=reader
<modify-keyspaces>=root

passwd.properties:
# some comments
writer=root
reader=root
root=root

cassandra-cli:
> use DynamicKeyspace root 'root';
DynamicKeyspace does not exist.

cassandra-env.sh:
JVM_OPTS="$JVM_OPTS -Dpasswd.properties=/etc/cassandra/passwd.properties -Daccess.properties=/etc/cassandra/access.properties"