Use a ServiceClient in identity v2, as well.
diff --git a/openstack/utils/client.go b/openstack/utils/client.go
index 6dda38f..7e3aa12 100644
--- a/openstack/utils/client.go
+++ b/openstack/utils/client.go
@@ -47,7 +47,8 @@
 		Options: ao,
 	}
 
-	ar, err := identity.Authenticate(ao)
+	c := &gophercloud.ServiceClient{Endpoint: ao.IdentityEndpoint}
+	ar, err := identity.Authenticate(c, ao)
 	if err != nil {
 		return client, err
 	}