Two authentication methods that would be used with a guest portal are social login and external portal. So the correct answers are A. social login and B. external portal.

According to the Cisco Catalyst 9800 Series Wireless Controller Software Configuration Guide2, two authentication methods that can be used with a guest portal are:

Social login, which allows guests to log in using their social media accounts such as Facebook, Twitter, or Google.

External portal, which allows guests to log in using an external web server that hosts a custom portal page.