Add custom SCEP configs (#27045)

For #26603 

This PR includes:
- Refactoring of NDES/SCEP verify/timeout logic for easier testing (with
dependency injection)
- Custom SCEP configs
- saving/deleting/updating of encrypted custom SCEP challenges
- validation call to custom SCEP server to verify connection
- Custom SCEP activities
- unit and integration tests for all of the above

This PR does not include the following:
- Changes file (in later PR)

# Checklist for submitter

- [x] Added/updated automated tests
- [x] Manual QA for all new/changed functionality

cmd/fleet/serve.go

@@ -732,6 +732,7 @@ the way that the Fleet server works.
 				mdmPushService,
 				cronSchedules,
 				wstepCertManager,
+				eeservice.NewSCEPConfigService(logger, nil),
 			)
 			if err != nil {
 				initFatal(err, "initializing service")
@@ -1163,7 +1164,7 @@ the way that the Fleet server works.
 
 			// SCEP proxy (for NDES, etc.)
 			if license.IsPremium() {
-				if err = service.RegisterSCEPProxy(rootMux, ds, logger); err != nil {
+				if err = service.RegisterSCEPProxy(rootMux, ds, logger, nil); err != nil {
 					initFatal(err, "setup SCEP proxy")
 				}
 			}

cmd/fleetctl/gitops_test.go

@@ -24,6 +24,7 @@ import (
 	"github.com/fleetdm/fleet/v4/server/mdm/testing_utils"
 	"github.com/fleetdm/fleet/v4/server/mock"
 	mdmmock "github.com/fleetdm/fleet/v4/server/mock/mdm"
+	scep_mock "github.com/fleetdm/fleet/v4/server/mock/scep"
 	"github.com/fleetdm/fleet/v4/server/ptr"
 	"github.com/fleetdm/fleet/v4/server/service"
 	"github.com/fleetdm/fleet/v4/server/test"
@@ -199,11 +200,15 @@ func TestGitOpsBasicGlobalPremium(t *testing.T) {
 	// Cannot run t.Parallel() because it sets environment variables
 
 	license := &fleet.LicenseInfo{Tier: fleet.TierPremium, Expiration: time.Now().Add(24 * time.Hour)}
+	scepConfig := &scep_mock.SCEPConfigService{}
+	scepConfig.ValidateSCEPURLFunc = func(_ context.Context, _ string) error { return nil }
+	scepConfig.ValidateNDESSCEPAdminURLFunc = func(_ context.Context, _ fleet.NDESSCEPProxyIntegration) error { return nil }
 	_, ds := runServerWithMockedDS(
 		t, &service.TestServerOpts{
-			License:         license,
-			KeyValueStore:   newMemKeyValueStore(),
-			EnableSCEPProxy: true,
+			License:           license,
+			KeyValueStore:     newMemKeyValueStore(),
+			EnableSCEPProxy:   true,
+			SCEPConfigService: scepConfig,
 		},
 	)