var ADMIN_USER = {username: "", password: ""};
var USERLIST = [
  {username: "", password: "", db: ""},
  {username: "", password: "", db: ""},
];


var admin_db = db.getSiblingDB('admin');
admin_db.createUser(
  {
    user: ADMIN_USER.username,
    pwd: ADMIN_USER.password,
    roles: [ { role: "userAdminAnyDatabase", db: "admin" } ]
  }
);

for (var i = 0; i < USERLIST.length; i++){
  var user = USERLIST[i];
  var user_db = db.getSiblingDB(user.db);
  user_db.users.insert({username: user.username});
  user_db.createUser({
    user: user.username,
    pwd: user.password,
    roles: [ { role: "readWrite", db: user.db } ]
  });
}