OAuth client: harden SEP-2352/SEP-2350 edge cases; fix conformance comment #2908

Job	Run time
checks / readme-snippets	11s
checks / pre-commit	40s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 8s
checks / test (3.10, locked, ubuntu-latest)	1m 2s
checks / test (3.10, lowest-direct, ubuntu-latest)	1m 1s
checks / test (3.12, locked, windows-latest)	1m 36s
checks / test (3.11, lowest-direct, windows-latest)	1m 26s
checks / test (3.13, lowest-direct, ubuntu-latest)	53s
checks / test (3.10, lowest-direct, windows-latest)	1m 30s
checks / test (3.11, lowest-direct, ubuntu-latest)	1m 6s
checks / test (3.11, locked, windows-latest)	1m 24s
checks / test (3.12, lowest-direct, windows-latest)	1m 34s
checks / test (3.11, locked, ubuntu-latest)	51s
checks / test (3.10, locked, windows-latest)	1m 42s
checks / test (3.12, locked, ubuntu-latest)	1m 0s
checks / test (3.13, locked, ubuntu-latest)	59s
checks / test (3.14, lowest-direct, windows-latest)	1m 25s
checks / test (3.14, lowest-direct, ubuntu-latest)	59s
checks / test (3.13, locked, windows-latest)	1m 23s
checks / test (3.14, locked, ubuntu-latest)	2m 0s
checks / test (3.13, lowest-direct, windows-latest)	1m 33s
checks / test (3.14, locked, windows-latest)	2m 17s
all-green	5s
	27m 45s

Provide feedback