feat: fully support Basic Authorization header at token request #4020

Job	Run time
checks / readme-snippets	10s
checks / pre-commit	31s
checks / test (3.10, lowest-direct, ubuntu-latest)	48s
checks / test (3.10, highest, windows-latest)	2m 8s
checks / test (3.11, lowest-direct, windows-latest)	2m 29s
checks / test (3.11, lowest-direct, ubuntu-latest)	45s
checks / test (3.10, highest, ubuntu-latest)	48s
checks / test (3.11, highest, windows-latest)	2m 29s
checks / test (3.11, highest, ubuntu-latest)	47s
checks / test (3.13, highest, windows-latest)	2m 28s
checks / test (3.10, lowest-direct, windows-latest)	2m 15s
checks / test (3.13, highest, ubuntu-latest)	48s
checks / test (3.12, lowest-direct, windows-latest)	3m 47s
checks / test (3.13, lowest-direct, windows-latest)	2m 19s
checks / test (3.12, lowest-direct, ubuntu-latest)	51s
checks / test (3.14, highest, ubuntu-latest)	1m 14s
checks / test (3.14, highest, windows-latest)	2m 13s
checks / test (3.12, highest, ubuntu-latest)	52s
checks / test (3.13, lowest-direct, ubuntu-latest)	42s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 6s
checks / test (3.14, lowest-direct, windows-latest)	2m 33s
checks / test (3.12, highest, windows-latest)	3m 23s
	35m 26s

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