Authority simply refers to the author(s). It is important to know who these people or organizations are and what makes them worth your time. The Internet has done a marvelous thing in allowing anyone to make public their opinions and thoughts, but that is exactly why it is important to know who you are getting your information from.
One way to help identify who the author is is to look at the URL especially the first part which holds the top level domain. Make sure it doesn't have a top level domain that causes you to have warning such as: http://kukluxklan.net/ or http://www.rip-you-off.com/.
Can't find an author or organization responsible for the content? DON'T USE IT!!!
Some Questions to Ask
Trying to find the author? Look for these.
Verify the information you find about the author(s). Do a quick Google search to see what others are saying about them. Is there contradicting information out there? Are they being linked or used by other people and sites that may discredit them?