Adopt reviewer's advices

examples/python/auth/BUILD.bazel

@@ -13,7 +13,7 @@
 # limitations under the License.
 
 filegroup(
-    name = "_credentails_files",
+    name = "_credentials_files",
     testonly = 1,
     srcs = [
         "credentials/localhost.key",
@@ -26,13 +26,13 @@ py_library(
     name = "_credentials",
     testonly = 1,
     srcs = ["_credentials.py"],
-    data = [":_credentails_files"],
+    data = [":_credentials_files"],
 )
 
 py_binary(
-    name = "customize_auth_client",
+    name = "customized_auth_client",
     testonly = 1,
-    srcs = ["customize_auth_client.py"],
+    srcs = ["customized_auth_client.py"],
     deps = [
         ":_credentials",
         "//src/python/grpcio/grpc:grpcio",
@@ -41,9 +41,9 @@ py_binary(
 )
 
 py_binary(
-    name = "customize_auth_server",
+    name = "customized_auth_server",
     testonly = 1,
-    srcs = ["customize_auth_server.py"],
+    srcs = ["customized_auth_server.py"],
     deps = [
         ":_credentials",
         "//src/python/grpcio/grpc:grpcio",
@@ -58,8 +58,8 @@ py_test(
     deps = [
         "//src/python/grpcio/grpc:grpcio",
         "//examples:py_helloworld",
-        ":customize_auth_client",
-        ":customize_auth_server",
+        ":customized_auth_client",
+        ":customized_auth_server",
         ":_credentials",
     ],
 )

examples/python/auth/README.md

@@ -2,7 +2,9 @@
 
 ## Check Our Guide First
 
-For most common usage of authentication in gRPC Python, please see our [Authentication](https://grpc.io/docs/guides/auth/) guide's Python section, it includes:
+For most common usage of authentication in gRPC Python, please see our
+[Authentication](https://grpc.io/docs/guides/auth/) guide's Python section. The
+Guide includes following scenarios:
 
 1. Server SSL credential setup
 2. Client SSL credential setup
@@ -13,11 +15,14 @@ Also, the guide talks about gRPC specific credential types.
 
 ### Channel credentials
 
-Channel credentials are attached to a `Channel` object, the most common use case are SSL credentials.
+Channel credentials are attached to a `Channel` object, the most common use case
+are SSL credentials.
 
 ### Call credentials
 
-Call credentials are attached to a `Call` object (corresponding to an RPC). Under the hood, the call credentials is a function that takes in information of the RPC and modify metadata through callback.
+Call credentials are attached to a `Call` object (corresponding to an RPC).
+Under the hood, the call credentials is a function that takes in information of
+the RPC and modify metadata through callback.
 
 ## About This Example
 
@@ -28,7 +33,16 @@ This example focuses on extending gRPC authentication mechanism:
 
 ## AuthMetadataPlugin: Manipulate metadata for each call
 
-Unlike TLS/SSL based authentication, the authentication extension in gRPC Python lives in a much higher level of abstraction. It relies on the transmit of metadata (HTTP Header) between client and server. gRPC Python provides a way to intercept an RPC and append authentication related metadata through [`AuthMetadataPlugin`](https://grpc.github.io/grpc/python/grpc.html#grpc.AuthMetadataPlugin).
+Unlike TLS/SSL based authentication, the authentication extension in gRPC Python
+lives at a much higher level of networking. It relies on the transmission of
+metadata (HTTP Header) between client and server, instead of alternating the
+transport protocol.
+
+gRPC Python provides a way to intercept an RPC and append authentication related
+metadata through
+[`AuthMetadataPlugin`](https://grpc.github.io/grpc/python/grpc.html#grpc.AuthMetadataPlugin).
+Those in need of a custom authentication method may simply provide a concrete
+implementation of the following interface:
 
 ```Python
 class AuthMetadataPlugin:
@@ -46,3 +60,53 @@ class AuthMetadataPlugin:
             synchronously or asynchronously.
         """
 ```
+
+Then pass the instance of the concrete implementation to
+`grpc.metadata_call_credentials` function to be converted into a
+`CallCredentials` object. Please NOTE that it is possible to pass a Python
+function object directly, but we recommend to inherit from the base class to
+ensure implementation correctness.
+
+
+```Python
+def metadata_call_credentials(metadata_plugin, name=None):
+    """Construct CallCredentials from an AuthMetadataPlugin.
+
+    Args:
+      metadata_plugin: An AuthMetadataPlugin to use for authentication.
+      name: An optional name for the plugin.
+
+    Returns:
+      A CallCredentials.
+    """
+```
+
+The `CallCredentials` object can be passed directly into an RPC like:
+
+```Python
+call_credentials = grpc.metadata_call_credentials(my_foo_plugin)
+stub.FooRpc(request, credentials=call_credentials)
+```
+
+Or you can use `ChannelCredentials` and `CallCredentials` at the same time by
+combining them:
+
+```Python
+channel_credentials = ...
+call_credentials = ...
+composite_credentials = grpc.composite_channel_credentials(
+    channel_credential,
+    call_credentials)
+channel = grpc.secure_channel(server_address, composite_credentials)
+```
+
+It is also possible to apply multiple `CallCredentials` to a single RPC:
+
+```Python
+call_credentials_foo = ...
+call_credentials_bar = ...
+call_credentials = grpc.composite_call_credentials(
+    call_credentials_foo,
+    call_credentials_bar)
+stub.FooRpc(request, credentials=call_credentials)
+```

examples/python/auth/customized_auth_client.py

@@ -32,7 +32,7 @@ _LOGGER.setLevel(logging.INFO)
 _ONE_DAY_IN_SECONDS = 60 * 60 * 24
 
 _SERVER_ADDR_TEMPLATE = 'localhost:%d'
-_SIGNATURE_HEADER_KEY = 'x-signautre'
+_SIGNATURE_HEADER_KEY = 'x-signature'
 
 
 class AuthGateway(grpc.AuthMetadataPlugin):
@@ -96,7 +96,7 @@ def main():
     parser = argparse.ArgumentParser()
     parser.add_argument(
         '--port',
-        nargs=1,
+        nargs='?',
         type=int,
         default=50051,
         help='the address of server')

examples/python/auth/customized_auth_server.py

@@ -34,7 +34,7 @@ _LOGGER.setLevel(logging.INFO)
 _ONE_DAY_IN_SECONDS = 60 * 60 * 24
 
 _LISTEN_ADDRESS_TEMPLATE = 'localhost:%d'
-_SIGNATURE_HEADER_KEY = 'x-signautre'
+_SIGNATURE_HEADER_KEY = 'x-signature'
 
 
 class SignatureValidationInterceptor(grpc.ServerInterceptor):
@@ -61,8 +61,7 @@ class SignatureValidationInterceptor(grpc.ServerInterceptor):
 
 class SimpleGreeter(helloworld_pb2_grpc.GreeterServicer):
 
-    @staticmethod
-    def SayHello(request, unused_context):
+    def SayHello(self, request, unused_context):
         return helloworld_pb2.HelloReply(message='Hello, %s!' % request.name)
 
 
@@ -86,19 +85,21 @@ def run_server(port):
         _credentials.SERVER_CERTIFICATE,
     ),))
 
-    # Pass down credentails
+    # Pass down credentials
     port = server.add_secure_port(_LISTEN_ADDRESS_TEMPLATE % port,
                                   server_credentials)
 
     server.start()
-    yield port
-    server.stop(0)
+    try:
+        yield port
+    finally:
+        server.stop(0)
 
 
 def main():
     parser = argparse.ArgumentParser()
     parser.add_argument(
-        '--port', nargs=1, type=int, default=50051, help='the listening port')
+        '--port', nargs='?', type=int, default=50051, help='the listening port')
     args = parser.parse_args()
 
     with run_server(args.port) as port: