feat: Migrate to HttpClient5 in `OAuth2Service` #2267

Job	Run time
Collect Context	4s
Run CodeQL Analysis	5m 10s
Check Formatting	29s
Run BlackDuck Scan	0s
Run Security Rating	0s
Test ${{ matrix.task.archetype }} Archetype	0s
Run ${{ matrix.task.name }} Analysis	0s
Test	0s
Build	-3s
	5m 40s

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