Add conformance auth server for OAuth server authentication testing #4035

Job	Run time
checks / pre-commit	21s
checks / readme-snippets	12s
checks / test (3.11, highest, ubuntu-latest)	48s
checks / test (3.11, highest, windows-latest)	2m 37s
checks / test (3.10, lowest-direct, windows-latest)	2m 19s
checks / test (3.12, lowest-direct, ubuntu-latest)	49s
checks / test (3.12, lowest-direct, windows-latest)	3m 32s
checks / test (3.10, highest, ubuntu-latest)	47s
checks / test (3.10, highest, windows-latest)	2m 23s
checks / test (3.11, lowest-direct, windows-latest)	2m 34s
checks / test (3.12, highest, windows-latest)	3m 31s
checks / test (3.12, highest, ubuntu-latest)	52s
checks / test (3.10, lowest-direct, ubuntu-latest)	50s
checks / test (3.11, lowest-direct, ubuntu-latest)	47s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 8s
checks / test (3.13, highest, windows-latest)	2m 39s
checks / test (3.13, highest, ubuntu-latest)	46s
checks / test (3.13, lowest-direct, windows-latest)	2m 21s
checks / test (3.14, highest, windows-latest)	2m 26s
checks / test (3.14, highest, ubuntu-latest)	1m 17s
checks / test (3.13, lowest-direct, ubuntu-latest)	43s
checks / test (3.14, lowest-direct, windows-latest)	2m 12s
	35m 54s

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