Fix partial declaration of authentication.

provider/label/partial.go

@@ -109,6 +109,8 @@ func GetAuth(labels map[string]string) *types.Auth {
 		auth.Digest = getAuthDigest(labels)
 	} else if HasPrefix(labels, TraefikFrontendAuthForward) {
 		auth.Forward = getAuthForward(labels)
+	} else {
+		return nil
 	}
 
 	return auth

provider/label/partial_test.go

@@ -732,6 +732,13 @@ func TestGetAuth(t *testing.T) {
 			labels:   map[string]string{},
 			expected: nil,
 		},
+		{
+			desc: "should return nil when no real auth",
+			labels: map[string]string{
+				TraefikFrontendAuthHeaderField: "myHeaderField",
+			},
+			expected: nil,
+		},
 		{
 			desc: "should return a basic auth",
 			labels: map[string]string{