Implement signature verification api #777

Job	Run time
docker-build	37s
test	6m 6s
build (linux, amd64)	34s
lint	58s
build (linux, 386)	31s
build (linux, arm)	30s
build (linux, arm64)	31s
build (darwin, amd64)	32s
build (darwin, arm64)	38s
build (windows, amd64)	30s
build (windows, 386)	35s
build (windows, arm)	30s
build (windows, arm64)	30s
integration-test-serverside (f0023141ec429d912e329665f937d05b178a3fee)	1m 45s
integration-test-clientside (v0.13.2)	2m 4s
analyze	1m 35s
	18m 26s

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