FAPI: Fix length check in auth callback. #714

Job	Run time
test-coverage	5m 12s
scanbuild	6m 41s
coverity-test	0s
build-test (ubuntu-20.04, gcc)	4m 32s
test-fuzz	2m 38s
build-test (ubuntu-20.04, clang)	4m 28s
test-mbedtls (ubuntu-20.04)	3m 13s
test-no-crypto-build	1m 19s
build-test (fedora-32, gcc)	4m 46s
test-mbedtls (ubuntu-22.04-mbedtls-3.1)	2m 53s
test-tcti-config	14m 41s
build-test (fedora-32, clang)	5m 13s
build-test (opensuse-leap, gcc)	4m 43s
build-test (opensuse-leap, clang)	4m 50s
build-test (ubuntu-22.04, gcc)	4m 25s
build-test (ubuntu-22.04, clang)	4m 56s
build-test (alpine-3.15, gcc)	3m 58s
build-test (alpine-3.15, clang)	5m 0s
	1h 23m 28s

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