implemented OAuth client credentials flow #520

Job	Run time
vars	1s
sites / Deploy sites	9m 1s
electron / electron (macos-latest)	9m 51s
tests / e2e-test (macos-latest)	13m 56s
tests / test (macos-latest)	10m 38s
electron / electron (ubuntu-latest)	9m 48s
tests / e2e-test (ubuntu-latest)	14m 21s
tests / test (ubuntu-latest)	12m 25s
electron / electron (windows-latest)	20m 43s
docker / docker	5m 48s
tests / api-e2e-test	7m 53s
	1h 54m 25s

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