feat: fully support Basic Authorization header at token request #4018

Job	Run time
checks / pre-commit	19s
checks / readme-snippets	10s
checks / test (3.11, lowest-direct, ubuntu-latest)	40s
checks / test (3.10, highest, ubuntu-latest)	45s
checks / test (3.10, highest, windows-latest)	2m 16s
checks / test (3.10, lowest-direct, ubuntu-latest)	46s
checks / test (3.11, lowest-direct, windows-latest)	2m 21s
checks / test (3.10, lowest-direct, windows-latest)	2m 14s
checks / test (3.13, highest, windows-latest)	2m 25s
checks / test (3.13, lowest-direct, ubuntu-latest)	43s
checks / test (3.12, lowest-direct, windows-latest)	3m 14s
checks / test (3.14, lowest-direct, windows-latest)	1m 57s
checks / test (3.13, highest, ubuntu-latest)	43s
checks / test (3.11, highest, windows-latest)	3m 1s
checks / test (3.11, highest, ubuntu-latest)	47s
checks / test (3.12, highest, windows-latest)	3m 15s
checks / test (3.12, lowest-direct, ubuntu-latest)	51s
checks / test (3.13, lowest-direct, windows-latest)	2m 50s
checks / test (3.12, highest, ubuntu-latest)	50s
checks / test (3.14, highest, ubuntu-latest)	1m 12s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 4s
checks / test (3.14, highest, windows-latest)	2m 34s
	34m 57s

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