[Python example] Add example for TLS (#34116)

Add example for TLS.

<!--

If you know who should review your pull request, please assign it to
that
person, otherwise the pull request would get assigned randomly.

If your pull request is for a specific language, please add the
appropriate
lang label.

-->

examples/python/auth/tls_client.py

@@ -0,0 +1,57 @@
+# Copyright 2023 The gRPC Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""Client of the Python example of TLS."""
+
+import logging
+
+import _credentials
+import grpc
+
+helloworld_pb2, helloworld_pb2_grpc = grpc.protos_and_services(
+    "helloworld.proto"
+)
+
+_LOGGER = logging.getLogger(__name__)
+_LOGGER.setLevel(logging.INFO)
+
+_PORT = 50051
+_SERVER_ADDR_TEMPLATE = "localhost:%d"
+
+
+def send_rpc(stub):
+    request = helloworld_pb2.HelloRequest(name="you")
+    try:
+        response = stub.SayHello(request)
+    except grpc.RpcError as rpc_error:
+        _LOGGER.error("Received error: %s", rpc_error)
+        return rpc_error
+    else:
+        _LOGGER.info("Received message: %s", response)
+        return response
+
+
+def main():
+    channel_credential = grpc.ssl_channel_credentials(
+        _credentials.ROOT_CERTIFICATE
+    )
+    with grpc.secure_channel(
+        _SERVER_ADDR_TEMPLATE % _PORT, channel_credential
+    ) as channel:
+        stub = helloworld_pb2_grpc.GreeterStub(channel)
+        send_rpc(stub)
+
+
+if __name__ == "__main__":
+    logging.basicConfig(level=logging.INFO)
+    main()

examples/python/auth/tls_server.py

@@ -0,0 +1,62 @@
+# Copyright 2023 The gRPC Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""Server of the Python example of TLS."""
+
+from concurrent import futures
+import logging
+
+import _credentials
+import grpc
+
+helloworld_pb2, helloworld_pb2_grpc = grpc.protos_and_services(
+    "helloworld.proto"
+)
+
+_LOGGER = logging.getLogger(__name__)
+_LOGGER.setLevel(logging.INFO)
+
+_PORT = 50051
+_LISTEN_ADDRESS_TEMPLATE = "localhost:%d"
+
+
+class SimpleGreeter(helloworld_pb2_grpc.GreeterServicer):
+    def SayHello(self, request, unused_context):
+        return helloworld_pb2.HelloReply(message="Hello, %s!" % request.name)
+
+
+def serve():
+    server = grpc.server(futures.ThreadPoolExecutor())
+    helloworld_pb2_grpc.add_GreeterServicer_to_server(SimpleGreeter(), server)
+
+    # Loading credentials
+    server_credentials = grpc.ssl_server_credentials(
+        (
+            (
+                _credentials.SERVER_CERTIFICATE_KEY,
+                _credentials.SERVER_CERTIFICATE,
+            ),
+        )
+    )
+
+    # Pass down credentials
+    server.add_secure_port(_LISTEN_ADDRESS_TEMPLATE % _PORT, server_credentials)
+
+    server.start()
+    logging.info("Server is listening at port :%d", _PORT)
+    server.wait_for_termination()
+
+
+if __name__ == "__main__":
+    logging.basicConfig(level=logging.INFO)
+    serve()