Auth: Add alpha version of the Extended JWT client (#67999)

* initial commit

* Add tests, add configuration options

* Extend signingkeys.Service with GetServerPublicKey method

* Add, cleanup tests

* Add tests for entitlements claim

* Fix linting errors

* Suggestion to use a struct to extend the claims

(cherry picked from commit 8078b99f1d57c9426a15693d850c1ca5f0432cbe)

* Add requested changes

Co-authored-by: Gabriel MABILLE <gamab@users.noreply.github.com>

* Add test for orgID check

* Cleanup

---------

Co-authored-by: Gabriel MABILLE <gamab@users.noreply.github.com>

pkg/services/authn/authnimpl/service.go

@@ -31,6 +31,7 @@ import (
 	"github.com/grafana/grafana/pkg/services/org"
 	"github.com/grafana/grafana/pkg/services/quota"
 	"github.com/grafana/grafana/pkg/services/rendering"
+	"github.com/grafana/grafana/pkg/services/signingkeys"
 	"github.com/grafana/grafana/pkg/services/user"
 	"github.com/grafana/grafana/pkg/setting"
 	"github.com/grafana/grafana/pkg/util/errutil"
@@ -63,6 +64,7 @@ func ProvideService(
 	features *featuremgmt.FeatureManager, oauthTokenService oauthtoken.OAuthTokenService,
 	socialService social.Service, cache *remotecache.RemoteCache,
 	ldapService service.LDAP, registerer prometheus.Registerer,
+	signingKeysService signingkeys.Service,
 ) authn.Service {
 	s := &Service{
 		log:            log.New("authn.service"),
@@ -128,6 +130,10 @@ func ProvideService(
 		s.RegisterClient(clients.ProvideJWT(jwtService, cfg))
 	}
 
+	if s.cfg.ExtendedJWTAuthEnabled && features.IsEnabled(featuremgmt.FlagExternalServiceAuth) {
+		s.RegisterClient(clients.ProvideExtendedJWT(userService, cfg, signingKeysService))
+	}
+
 	for name := range socialService.GetOAuthProviders() {
 		oauthCfg := socialService.GetOAuthInfoProvider(name)
 		if oauthCfg != nil && oauthCfg.Enabled {