MongoDB shell version: 3.0.6
connecting to: admin
> db.createUser
function (userObj, writeConcern) {
    var name = userObj["user"];
    var cmdObj = {createUser:name};
    cmdObj = Object.extend(cmdObj, userObj);
    delete cmdObj["user"];

    this._modifyCommandToDigestPasswordIfNecessary(cmdObj, name);

    cmdObj["writeConcern"] = writeConcern ? writeConcern : _defaultWriteConcern;

    var res = this.runCommand(cmdObj);

    if (res.ok) {
        print("Successfully added user: " + getUserObjString(userObj));
        return;
    }

    if (res.errmsg == "no such cmd: createUser") {
        throw Error("'createUser' command not found.  This is most likely because you are " +
                    "talking to an old (pre v2.6) MongoDB server");
    }

    if (res.errmsg == "timeout") {
        throw Error("timed out while waiting for user authentication to replicate - " +
                    "database will not be fully secured until replication finishes");
    }

    throw Error("couldn't add user: " + res.errmsg);
}
>

mongo localhost:27017/admin --authenticationDatabase admin -u siteUserAdmin -p password