Authentication Type — Definition

Authentication type is the APN setting that controls how your phone proves it's allowed to use the carrier's data connection, usually None, PAP, or CHAP.

Most consumer carriers use None, meaning no username or password is checked. Some, particularly certain prepaid or business plans, use PAP or CHAP along with a username and password.

In practice

Match whatever your carrier's page specifies. If it says None, leave the username and password blank too. If it lists PAP or CHAP, you'll have a username and password to enter alongside it. Mismatching this is a quiet cause of data that won't connect.