feat: add mtls feature (#917)

diff --git a/setup.py b/setup.py
index 4c740e6..6554583 100644
--- a/setup.py
+++ b/setup.py
@@ -39,7 +39,7 @@
     # currently upgrade their httplib2 version.
     # Please see https://github.com/googleapis/google-api-python-client/pull/841
     "httplib2>=0.9.2,<1dev",
-    "google-auth>=1.4.1",
+    "google-auth>=1.16.0",
     "google-auth-httplib2>=0.0.3",
     "google-api-core>=1.13.0,<2dev",
     "six>=1.6.1,<2dev",