feat: fully support Basic Authorization header at token request #4017

Job	Run time
checks / pre-commit	33s
checks / readme-snippets	11s
checks / test (3.11, lowest-direct, windows-latest)	2m 41s
checks / test (3.11, lowest-direct, ubuntu-latest)	44s
checks / test (3.10, lowest-direct, windows-latest)	2m 38s
checks / test (3.10, highest, ubuntu-latest)	46s
checks / test (3.13, lowest-direct, ubuntu-latest)	44s
checks / test (3.11, highest, ubuntu-latest)	48s
checks / test (3.14, lowest-direct, windows-latest)	2m 15s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 9s
checks / test (3.10, highest, windows-latest)	2m 19s
checks / test (3.13, highest, windows-latest)	2m 21s
checks / test (3.12, highest, windows-latest)	3m 20s
checks / test (3.10, lowest-direct, ubuntu-latest)	48s
checks / test (3.12, lowest-direct, windows-latest)	3m 20s
checks / test (3.12, lowest-direct, ubuntu-latest)	52s
checks / test (3.13, highest, ubuntu-latest)	44s
checks / test (3.13, lowest-direct, windows-latest)	2m 19s
checks / test (3.11, highest, windows-latest)	2m 31s
checks / test (3.14, highest, windows-latest)	2m 49s
checks / test (3.14, highest, ubuntu-latest)	1m 7s
checks / test (3.12, highest, ubuntu-latest)	56s
	35m 55s

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