add topic frontmatter to articles (#18245)

content/github/authenticating-to-github/preventing-unauthorized-access.md

@@ -6,6 +6,9 @@ redirect_from:
 versions:
   free-pro-team: '*'
   enterprise-server: '*'
+topics:
+  - identity
+  - access management
 ---
 
 {% data variables.product.product_name %} requires a password to perform sensitive actions, such as adding new SSH keys, authorizing applications, or modifying team members.