Accumulate OAuth scopes across step-up authorization challenges #2566

Job	Run time
build (windows-latest, Debug)	4m 23s
build (ubuntu-latest, Release)	1m 33s
build (macos-latest, Release)	1m 24s
build (ubuntu-latest, Debug)	1m 43s
build (macos-latest, Debug)	1m 6s
build (windows-latest, Release)	3m 25s
publish-coverage	0s
	13m 34s

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