auth: improve ClientAuthenticator error messaging #2331

Job	Run time
checks / readme-snippets	12s
checks / test (3.10, lowest-direct, windows-latest)	2m 30s
checks / test (3.12, locked, windows-latest)	3m 16s
checks / test (3.13, locked, windows-latest)	2m 45s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 31s
checks / test (3.11, locked, windows-latest)	2m 44s
checks / test (3.14, lowest-direct, windows-latest)	3m 2s
checks / test (3.11, lowest-direct, ubuntu-latest)	1m 3s
checks / pre-commit	20s
checks / test (3.14, locked, ubuntu-latest)	2m 28s
checks / test (3.14, locked, windows-latest)	3m 38s
checks / test (3.11, lowest-direct, windows-latest)	2m 44s
checks / test (3.13, lowest-direct, ubuntu-latest)	1m 2s
checks / test (3.11, locked, ubuntu-latest)	1m 1s
checks / test (3.12, lowest-direct, ubuntu-latest)	1m 12s
checks / test (3.12, lowest-direct, windows-latest)	3m 30s
checks / test (3.13, locked, ubuntu-latest)	59s
checks / test (3.13, lowest-direct, windows-latest)	3m 36s
checks / test (3.10, locked, windows-latest)	2m 27s
checks / test (3.10, locked, ubuntu-latest)	59s
checks / test (3.12, locked, ubuntu-latest)	1m 9s
checks / test (3.10, lowest-direct, ubuntu-latest)	1m 4s
all-green	4s
	43m 16s

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