Implement RFC 7523 JWT flows #2782

Job	Run time
checks / pre-commit	26s
checks / readme-snippets	11s
checks / test (3.10, lowest-direct, windows-latest)	1m 26s
checks / test (3.10, lowest-direct, ubuntu-latest)	35s
checks / test (3.11, highest, windows-latest)	1m 19s
checks / test (3.11, lowest-direct, windows-latest)	1m 25s
checks / test (3.10, highest, windows-latest)	1m 33s
checks / test (3.10, highest, ubuntu-latest)	34s
checks / test (3.12, highest, ubuntu-latest)	32s
checks / test (3.12, highest, windows-latest)	1m 24s
checks / test (3.12, lowest-direct, windows-latest)	1m 46s
checks / test (3.13, lowest-direct, windows-latest)	1m 17s
checks / test (3.13, lowest-direct, ubuntu-latest)	39s
checks / test (3.11, lowest-direct, ubuntu-latest)	32s
checks / test (3.11, highest, ubuntu-latest)	35s
checks / test (3.13, highest, windows-latest)	1m 30s
checks / test (3.13, highest, ubuntu-latest)	33s
checks / test (3.12, lowest-direct, ubuntu-latest)	32s
	16m 49s

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