The project is clearly licensed under the BSD License. See the LICENSE file and the in-file comments below. You can't both license under the standard BSD License and carve out commercial usage.
""" authlib ~~~~~~~
The ultimate Python library in building OAuth 1.0, OAuth 2.0 and OpenID
Connect clients and providers. It covers from low level specification
implementation to high level framework integrations.
:copyright: (c) 2017 by Hsiaoming Yang.
:license: BSD, see LICENSE for more details.
"""
Re:Authlib: Python Authentication
by notpushkin on Monday June 26, 2023 @01:27PM
(#36482867)
It used to be AGPL, but they switched to BSD some time ago (and I think just forgot to change wording on the commercial license offering).
Or $2,000 a year if your company wants to pay by invoice.