Full Definition or Meme
When the exact nature of the user request is unknown, it is best to try Authentication in the least obtrusive manner, which is typically not at the highest level they might need later in the interchange.
Then general use case is where trust elevation must occur during the
An anti-use case was discovered when the NSA funded the Blacker
When mobile device became common it was early realized that the blacker solution was not feasible and progressive authentication was proposed for mobile y devices and later specifically for Android devices.
An alternative definition of progressive authentication is a suite of authentication tests which can be selected to be run at a single time with a Trust Vector that can be tested by the authorization service.
NIST in now in the thrid update to their Digital Identity Guidelines  where they still insist, against all evidence to the contrary that "digital identity is the unique representation of a subject engaged in an online transaction."
- Tom Jones Trust Elevation Use Case https://wiki.idesg.org/wiki/index.php?title=Trust_Elevation_Use_Case
- Oriana Riva +3 Progressive authentication: deciding when to authenticate on mobile phones Published in: Proceedings Security'12 Proceedings of the 21st USENIX conference on Security symposium Pages 15-15 Bellevue, WA August 08 - 10, 2012, http://feihu.eng.ua.edu/NSF_CPS/year1/SP_paper1.pdf
- Jeffrey Warren, +3, Progressive Authentication on Android https://css.csail.mit.edu/6.858/2013/projects/jtwarren-vkgdaddy-vedha-vvelaga.pdf
- NIST Digital Identity Guidelines https://doi.org/10.6028/NIST.SP.800-63-3