feat(auth): add Authlib-backed OAuth adapter (related to #1240) #1211

Job	Run time
checks / readme-snippets	15s
checks / pre-commit	39s
checks / test (3.10, locked, ubuntu-latest)	54s
checks / test (3.10, lowest-direct, windows-latest)	2m 50s
checks / test (3.11, lowest-direct, ubuntu-latest)	58s
checks / test (3.11, lowest-direct, windows-latest)	2m 36s
checks / test (3.10, lowest-direct, ubuntu-latest)	1m 1s
checks / test (3.14, locked, windows-latest)	3m 43s
checks / test (3.12, locked, windows-latest)	3m 26s
checks / test (3.10, locked, windows-latest)	2m 20s
checks / test (3.12, lowest-direct, windows-latest)	3m 30s
checks / test (3.13, lowest-direct, ubuntu-latest)	59s
checks / test (3.13, locked, windows-latest)	2m 38s
checks / test (3.13, lowest-direct, windows-latest)	2m 32s
checks / test (3.12, locked, ubuntu-latest)	59s
checks / test (3.11, locked, windows-latest)	2m 32s
checks / test (3.11, locked, ubuntu-latest)	54s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 3s
checks / test (3.13, locked, ubuntu-latest)	51s
checks / test (3.14, lowest-direct, windows-latest)	2m 43s
checks / test (3.14, locked, ubuntu-latest)	2m 13s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 24s
all-green	6s
	41m 6s

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