Authentication to WEB site with bar code by mobile application when browsing on mobile device?

Mobile application can scan bar code, combine user secret and send request to server to authorize access to web page, showing bar code.

How should we deal with situation when customer wants to authorize to web size via bar code on mobile device itself?

You obviously can't point camera to screen )) User can make screenshot and process it within app but that is not UX friendly.

Are there some web standards to support web page authentication workflow with preinstalled application on mobile device?