Hello David
Indeed, according to RFC 3768 and even the most recent VRRP RFC 5798, VRRP does not currently include any authentication. Indeed, an earlier version of VRRP included several types of authentication. However, according to both of the above RFCs:
Earlier version of the VRRP specification had several defined
authentication types [RFC2338]. These were removed in this
specification because operational experience showed that they did not
provide any real security and would only cause multiple masters to be
created.
However, Cisco has implemented a proprietary feature called VRRP Authentication that provides a way to add authentication to VRRP. More about how to configure that can be found in the lesson, as you have already mentioned, as well as in the following documentation:
It is important to note that because VRRP Authentication is a proprietary feature, it may not be supported on other vendor devices or be interoperable with other VRRP implementations. If you need to provide redundancy between devices from different vendors, you may want to consider using an industry-standard protocol such as GLBP (Gateway Load Balancing Protocol) which support authentication and are supported by multiple vendors.
I hope this has been helpful!
Laz