You're looking at StableBuild's Deleted PyPI mirror - where we index all deleted packages from the Python package registry.

flask-auth-client
0.0.6

This version was deleted from PyPI around 2023-10-09. Installing fails with:
$ pip3 install flask-auth-client==0.0.6 ERROR: Could not find a version that satisfies the requirement flask-auth-client==0.0.6

Install through StableBuild

You can install this package from StableBuild's PyPI snapshots from before the version was deleted:
pip3 install \ -i https://YOUR_API_KEY.pypimirror.stablebuild.com/2023-10-08/ \ flask-auth-client==0.0.6
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Or, download files manually

And install manually via pip: