To authenticate.

"You can't post messages on the site unless you're authed."

Something which validates or confirms the authenticity of something

Proof of the identity of a user logging on to some network

A hallmark or assay-mark on a piece of metalwork

One who commands absolute obedience to his or her authority.

"The dictator was an authoritarian."

One who follows and is excessively obedient to authority.

"2006, Robert Altemeyer, The Authoritarians"

Permission.

"I've got authorization. Call the office and you'll see."

An act of authorizing.

(A document giving) formal sanction, permission or warrant.

"Can I see your authorization?"

Permission, possibly limited, to spend funds for a specific budgetary purpose.

"We've had the authorization for years, but we've never gotten an appropriation."