The Defense Dept already does this: CAC/common access cards [1]. Create a civilian root and do it already. A PIV/CAC can also be used as an auth factor with Login.gov [2].
[1] https://www.cac.mil/common-access-card/
[2] https://www.login.gov/help/get-started/authentication-method... (Physical PIV (personal identity verification) cards or CACs (common access cards) are secure options for federal government employees and military personnel. These cards, with encrypted chip technology, are resistant to phishing and difficult to hack if stolen.)