fix: expose ssl credentials from transport (#677)

Expose ssl credentials from transport.

This is used to fix pubsub client [mtls issue](googleapis/python-pubsub#224). Pubsub client creates its own transport so mtls is completely missing. The solution would be taking the ssl credentials from the auto-generated client's transport and passing it when the handwritten client creates the transport.

Author: arithmetic1728

gapic/ads-templates/%namespace/%name/%version/%sub/services/%service/transports/grpc.py.j2

@@ -88,13 +88,16 @@ class {{ service.name }}GrpcTransport({{ service.name }}Transport):
           google.auth.exceptions.MutualTLSChannelError: If mutual TLS transport
               creation failed for any reason.
         """
+        self._ssl_channel_credentials = ssl_channel_credentials
+
         if channel:
             # Sanity check: Ensure that channel and credentials are not both
             # provided.
             credentials = False
 
             # If a channel was explicitly provided, set it.
             self._grpc_channel = channel
+            self._ssl_channel_credentials = None
         elif api_mtls_endpoint:
             warnings.warn("api_mtls_endpoint and client_cert_source are deprecated", DeprecationWarning)
 
@@ -122,6 +125,7 @@ class {{ service.name }}GrpcTransport({{ service.name }}Transport):
                 scopes=scopes or self.AUTH_SCOPES,
                 quota_project_id=quota_project_id,
             )
+            self._ssl_channel_credentials = ssl_credentials
         else:
             host = host if ":" in host else host + ":443"
 

gapic/ads-templates/tests/unit/gapic/%name_%version/%sub/test_%service.py.j2

@@ -708,6 +708,7 @@ def test_{{ service.name|snake_case }}_grpc_transport_channel():
     )
     assert transport.grpc_channel == channel
     assert transport._host == "squid.clam.whelk:443"
+    assert transport._ssl_channel_credentials == None
 
 
 @pytest.mark.parametrize("transport_class", [transports.{{ service.grpc_transport_name }}])
@@ -749,6 +750,7 @@ def test_{{ service.name|snake_case }}_transport_channel_mtls_with_client_cert_s
                 quota_project_id=None,
             )
             assert transport.grpc_channel == mock_grpc_channel
+            assert transport._ssl_channel_credentials == mock_ssl_cred
 
 
 @pytest.mark.parametrize("transport_class", [transports.{{ service.grpc_transport_name }},])

gapic/templates/%namespace/%name_%version/%sub/services/%service/transports/grpc.py.j2

@@ -96,13 +96,16 @@ class {{ service.name }}GrpcTransport({{ service.name }}Transport):
           google.api_core.exceptions.DuplicateCredentialArgs: If both ``credentials``
               and ``credentials_file`` are passed.
         """
+        self._ssl_channel_credentials = ssl_channel_credentials
+
         if channel:
             # Sanity check: Ensure that channel and credentials are not both
             # provided.
             credentials = False
 
             # If a channel was explicitly provided, set it.
             self._grpc_channel = channel
+            self._ssl_channel_credentials = None
         elif api_mtls_endpoint:
             warnings.warn("api_mtls_endpoint and client_cert_source are deprecated", DeprecationWarning)
 
@@ -130,6 +133,7 @@ class {{ service.name }}GrpcTransport({{ service.name }}Transport):
                 scopes=scopes or self.AUTH_SCOPES,
                 quota_project_id=quota_project_id,
             )
+            self._ssl_channel_credentials = ssl_credentials
         else:
             host = host if ":" in host else host + ":443"
 

gapic/templates/%namespace/%name_%version/%sub/services/%service/transports/grpc_asyncio.py.j2

@@ -140,13 +140,16 @@ class {{ service.grpc_asyncio_transport_name }}({{ service.name }}Transport):
           google.api_core.exceptions.DuplicateCredentialArgs: If both ``credentials``
               and ``credentials_file`` are passed.
         """
+        self._ssl_channel_credentials = ssl_channel_credentials
+
         if channel:
             # Sanity check: Ensure that channel and credentials are not both
             # provided.
             credentials = False
 
             # If a channel was explicitly provided, set it.
             self._grpc_channel = channel
+            self._ssl_channel_credentials = None
         elif api_mtls_endpoint:
             warnings.warn("api_mtls_endpoint and client_cert_source are deprecated", DeprecationWarning)
 
@@ -174,6 +177,7 @@ class {{ service.grpc_asyncio_transport_name }}({{ service.name }}Transport):
                 scopes=scopes or self.AUTH_SCOPES,
                 quota_project_id=quota_project_id,
             )
+            self._ssl_channel_credentials = ssl_credentials
         else:
             host = host if ":" in host else host + ":443"
 

gapic/templates/tests/unit/gapic/%name_%version/%sub/test_%service.py.j2

@@ -1184,6 +1184,7 @@ def test_{{ service.name|snake_case }}_grpc_transport_channel():
     )
     assert transport.grpc_channel == channel
     assert transport._host == "squid.clam.whelk:443"
+    assert transport._ssl_channel_credentials == None
 
 
 def test_{{ service.name|snake_case }}_grpc_asyncio_transport_channel():
@@ -1196,6 +1197,7 @@ def test_{{ service.name|snake_case }}_grpc_asyncio_transport_channel():
     )
     assert transport.grpc_channel == channel
     assert transport._host == "squid.clam.whelk:443"
+    assert transport._ssl_channel_credentials == None
 
 
 @pytest.mark.parametrize("transport_class", [transports.{{ service.grpc_transport_name }}, transports.{{ service.grpc_asyncio_transport_name }}])
@@ -1237,6 +1239,7 @@ def test_{{ service.name|snake_case }}_transport_channel_mtls_with_client_cert_s
                 quota_project_id=None,
             )
             assert transport.grpc_channel == mock_grpc_channel
+            assert transport._ssl_channel_credentials == mock_ssl_cred
 
 
 @pytest.mark.parametrize("transport_class", [transports.{{ service.grpc_transport_name }}, transports.{{ service.grpc_asyncio_transport_name }}])