dashes not allowed in users, groups in cfengine3

If you try:

"""
body common control {
    bundlesequence => { "wwwdatatest" } ;
}

body perms user(username) {
    owners => { "$(username)" };

}

bundle agent wwwdatatest {
    files:
        "/tmp/www-data-test"
            perms => user("www-data");
}
"""

You get:

# /var/cfengine/bin/cf-promises -f ./file_breakage.cf
Validation: Scalar item in owners => { www-data } in rvalue is out of
bounds (value should match pattern [a-zA-Z0-9_$.]+)

Dashes are allowed in Linux (and some distros ship expecting them to work).

Patrick