user@ubuntu:/$ mongo
MongoDB shell version: 2.2.3
connecting to: test
> use mytest
switched to db mytest
> db.testcollection.insert({"message":"Hello, remote user!"})
> db.addUser('myuser', 'superpassword')
{ "n" : 0, "connectionId" : 2, "err" : null, "ok" : 1 }
{
    "user" : "myuser",
    "readOnly" : false,
    "pwd" : "ecb2c08916b34e477c33c10cec2ae416",
    "_id" : ObjectId("512c6d9dcc5d103a896944ae")
}
> db.testcollection.find()
{ "_id" : ObjectId("512c6d85cc5d103a896944ad"), "message" : "Hello, remote user!" }