How do we know that the author or authors are experts? Authority means that the creator of the information source is an expert in the field. The creator can be an author, multiple authors, or an organization, government agency, company, etc.
Examine the author's credentials
View their biographical information such as their curriculum vitae (C.V.), publication history, and the response their work has received from other experts in the field. Look for book reviews of the author's work. Where has their work been published and in what type of publication? Articles in scholarly journals will include an author's credentials and references.
If the creator is a company or organization, look for information about the organization on their website. Sometimes this is under an "About Us" link. You can search the library databases to see what other information is available about the company or organization. Consider aspects of reliability and validity when reviewing a company's stance.