Biometric boarding pass

I had never heard of this before.

Who or what is Clear?

Is Clear the one obtaining and probably storing the bio metric information?

Are they allowed to sell it?

Are they allowed to force you to use this or not fly in the present as this article is several years old

https://news.delta.com/delta-launches-biometrics-board-aircraft-reagan-washington-national-airport

https://wired.me/technology/privacy/emirates-facial-recognition/

article bio biometric information old privacy sell what is