use sigstore/sigstore instead of directly calling RSA/ECDSA verify ca…

…lls (#221)

Signed-off-by: Bob Callaway <bob.callaway@gmail.com>

go.mod

@@ -27,6 +27,7 @@ require (
 	github.com/prometheus/common v0.29.0 // indirect
 	github.com/prometheus/procfs v0.7.0 // indirect
 	github.com/rs/cors v1.8.0
+	github.com/sigstore/sigstore v1.0.0
 	github.com/spf13/cobra v1.2.1
 	github.com/spf13/pflag v1.0.5
 	github.com/spf13/viper v1.9.0
@@ -39,6 +40,5 @@ require (
 	golang.org/x/net v0.0.0-20210614182718-04defd469f4e
 	google.golang.org/genproto v0.0.0-20210828152312-66f60bf46e71
 	google.golang.org/protobuf v1.27.1
-	gopkg.in/square/go-jose.v2 v2.6.0 // indirect
 	gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b
 )