connectors: refactor filter code into a helper package

I hope I didn't miss any :D

Signed-off-by: Stephan Renatus <srenatus@chef.io>

connector/microsoft/microsoft.go

@@ -15,6 +15,7 @@ import (
 	"golang.org/x/oauth2"
 
 	"github.com/dexidp/dex/connector"
+	groups_pkg "github.com/dexidp/dex/pkg/groups"
 	"github.com/dexidp/dex/pkg/log"
 )
 
@@ -311,22 +312,9 @@ func (c *microsoftConnector) getGroups(ctx context.Context, client *http.Client,
 	}
 
 	// ensure that the user is in at least one required group
-	isInGroups := false
-	if len(c.groups) > 0 {
-		gs := make(map[string]struct{})
-		for _, g := range c.groups {
-			gs[g] = struct{}{}
-		}
-
-		for _, g := range groups {
-			if _, ok := gs[g]; ok {
-				isInGroups = true
-				break
-			}
-		}
-	}
-	if len(c.groups) > 0 && !isInGroups {
-		return nil, fmt.Errorf("microsoft: user %v not in required groups", userID)
+	filteredGroups := groups_pkg.Filter(groups, c.groups)
+	if len(c.groups) > 0 && len(filteredGroups) == 0 {
+		return nil, fmt.Errorf("microsoft: user %v not in any of the required groups", userID)
 	}
 
 	return