Initial working implementation

src/python/grpcio/grpc/__init__.py

@@ -1868,6 +1868,13 @@ def alts_server_credentials():
     return ServerCredentials(_cygrpc.server_credentials_alts())
 
 
+def google_default_channel_credentials():
+    """
+    TODO: Document.
+    """
+    return ChannelCredentials(_cygrpc.channel_credentials_google_default())
+
+
 def channel_ready_future(channel):
     """Creates a Future that tracks when a Channel is ready.
 

src/python/grpcio/grpc/_cython/_cygrpc/credentials.pyx.pxi

@@ -380,3 +380,16 @@ def server_credentials_alts():
   # Options can be destroyed as deep copy was performed.
   grpc_alts_credentials_options_destroy(c_options)
   return credentials
+
+cdef class GoogleDefaultChannelCredentials(ChannelCredentials):
+  cdef grpc_channel_credentials* _c_creds
+
+  def __cinit__(self):
+    self._c_creds = NULL
+
+  cdef grpc_channel_credentials *c(self) except *:
+    self._c_creds = grpc_google_default_credentials_create()
+    return self._c_creds
+
+def channel_credentials_google_default():
+  return GoogleDefaultChannelCredentials()

src/python/grpcio_tests/tests/interop/BUILD.bazel

@@ -12,7 +12,7 @@ py_library(
     ],
 )
 
-py_library(
+py_binary(
     name = "client",
     srcs = ["client.py"],
     imports = ["../../"],

src/python/grpcio_tests/tests/interop/client.py

@@ -51,6 +51,10 @@ def parse_interop_client_args():
                         default=False,
                         type=resources.parse_bool,
                         help='replace platform root CAs with ca.pem')
+    parser.add_argument('--custom_credentials_type',
+                        choices=["google_default_credentials"],
+                        default=None,
+                        help='use google default credentials')
     parser.add_argument('--server_host_override',
                         type=str,
                         help='the server host to which to claim to connect')
@@ -90,7 +94,16 @@ def get_secure_channel_parameters(args):
     call_credentials = _create_call_credentials(args)
 
     channel_opts = None
-    if args.use_tls:
+    if args.custom_credentials_type is not None:
+        if args.custom_credentials_type == "google_default_credentials":
+            channel_credentials = grpc.google_default_channel_credentials()
+            if call_credentials is not None:
+                channel_credentials = grpc.composite_channel_credentials(
+                    channel_credentials, call_credentials)
+        else:
+            raise ValueError("Unknown credentials type '{}'".format(
+                args.custom_credentials_type))
+    elif args.use_tls:
         if args.use_test_ca:
             root_certificates = resources.test_root_certificates()
         else:
@@ -115,7 +128,7 @@ def get_secure_channel_parameters(args):
 def _create_channel(args):
     target = '{}:{}'.format(args.server_host, args.server_port)
 
-    if args.use_tls or args.use_alts:
+    if args.use_tls or args.use_alts or args.custom_credentials_type is not None:
         channel_credentials, options = get_secure_channel_parameters(args)
         return grpc.secure_channel(target, channel_credentials, options)
     else:

src/python/grpcio_tests/tests_aio/interop/BUILD.bazel

@@ -62,6 +62,7 @@ py_binary(
     ],
 )
 
+# TODO: Pull out library to fix aio interop client.
 py_binary(
     name = "client",
     srcs = ["client.py"],