The Institute of World Politics kept a faculty page for Stefan A. Halper. An archive.ph capture is the résumé this site uses for titles and dates. It lists a Stanford B.A. (1967), an Oxford D.Phil. (1971), and a Cambridge Ph.D. (2004). It lists White House service in the 1970s, work for Sen. William Roth and the Joint Economic Committee, campaign policy roles in 1979–80, and Deputy Assistant Secretary of State for Politico-Military Affairs from 1981 to 1984.
The same line describes later work as a senior advisor at the Department of Defense and the Department of Justice (1984–2001) and then a Cambridge appointment. Those are self-described titles on a faculty bio. They are not a CIA personnel file. This site does not invent a staff-officer rank or a conviction.
Washington Examiner (May 12, 2019) later summarized the same arc — Nixon, Ford, Reagan White House; Cambridge director of American studies — in a profile written after he was named as an FBI informant. That profile is reporting and commentary. The IWP archive is the identity document.