feat(auth): add Authlib-backed OAuth adapter (related to #1240) #1063

Job	Run time
checks / pre-commit	36s
checks / readme-snippets	13s
checks / test (3.11, lowest-direct, ubuntu-latest)	1m 0s
checks / test (3.10, locked, windows-latest)	2m 7s
checks / test (3.10, lowest-direct, ubuntu-latest)	59s
checks / test (3.11, locked, windows-latest)	2m 36s
checks / test (3.10, locked, ubuntu-latest)	54s
checks / test (3.11, lowest-direct, windows-latest)	2m 35s
checks / test (3.11, locked, ubuntu-latest)	51s
checks / test (3.10, lowest-direct, windows-latest)	2m 19s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 3s
checks / test (3.14, lowest-direct, windows-latest)	2m 24s
checks / test (3.13, lowest-direct, windows-latest)	2m 39s
checks / test (3.14, locked, windows-latest)	3m 10s
checks / test (3.13, lowest-direct, ubuntu-latest)	56s
checks / test (3.13, locked, windows-latest)	2m 23s
checks / test (3.13, locked, ubuntu-latest)	54s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 22s
checks / test (3.12, locked, ubuntu-latest)	57s
checks / test (3.12, locked, windows-latest)	3m 16s
checks / test (3.14, locked, ubuntu-latest)	2m 18s
checks / test (3.12, lowest-direct, windows-latest)	3m 40s
all-green	5s
	39m 17s

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