https://en.wikipedia.org/wiki/Multi-factor_authentication :
- Something the user has - device/token
- Something the user knows - password/pin
- Something the user is - biometrics
https://en.wikipedia.org/wiki/Multi-factor_authentication :
Have you read Worm ( https://parahumans.wordpress.com/ ) or wandering inn ( https://wanderinginn.com/ ) ?
https://scholar.archive.org/