PouchDB / CouchDB / Cloudant PUT _security - couchdb

Question

PouchDB and Cloud-Cloudant setup.
Development environment: Ionic hybrid App (AngularJS).
Would like to create database and set up permission from code.
Tried
put _security but received error code 400. Only reserved document ids may start with underscore.
Refer to Cloudant API regarding modifying permission. But failed to implement. Anyone could eliminate about how to perform this?
https://docs.cloudant.com/authorization.html#modifying-permissions
Example of my code.
var attendanceSecurity = {
"_id": "_security",
"cloudant": {
"nobody": []
}
};
attendanceSecurity['cloudant'][user.id] = ["_reader","_writer","_replicator"];
var user2 = {
name: username,
password: password
};
var pouchOpts = {
skipSetup: false
};
var ajaxOpts = {
ajax: {
headers: {
Authorization: 'Basic ' + window.btoa(user2.name + ':' + user2.password)
}
}
};
var url = 'https://' + attendanceUsername + '.cloudant.com/' + user.id;
var db = new PouchDB(url, pouchOpts);
db.login(user2.name, user2.password, ajaxOpts).then(function() {
return db.allDocs();
}).then(function(docs) {
db.put(attendanceSecurity).then(function (response) {
// handle response
console.log(response);
}).catch(function (err) {
console.log(err);
});
console.log(docs);
}).catch(function(error) {
console.error(error);
});