Add support different grant types, add support updating of token without refresh_token

README.md

@@ -52,14 +52,33 @@ stub.FooRpc(request, credentials=call_credentials)
 
 ```python
 import grpc
-
+from oauthlib.oauth2 import Client
+from oauthlib.oauth2.rfc6749.parameters import prepare_token_request
 from auth import OAuth2Plugin
 from users.users_pb2 import GetRequest
 from users.users_pb2_grpc import UsersStub
- 
+
+# Могут быть использованы как встроенные клиенты, такие как WebApplicationClient, BackendApplicationClient, 
+# так и допускается реализовать собственный класс с кастомным поведением
+
+class ExtendedClient(Client):
+    def __init__(self, client_id, grant_type, username, password, **kwargs):
+        self.grant_type = grant_type
+        self.username = username
+        self.password = password
+        super(ExtendedClient, self).__init__(client_id, **kwargs)
+
+    def prepare_request_body(self, body='', scope=None, include_client_id=False, **kwargs):
+        kwargs['client_id'] = self.client_id
+        kwargs['include_client_id'] = include_client_id
+        return prepare_token_request(self.grant_type, body=body, username=self.username,
+                                     password=self.password, scope=scope, **kwargs)
+
 oauth2_plugin = OAuth2Plugin(
-    client_id='client_id', client_secret='client_secret', 
-    token_url='https://example.com/oauth/token', audience='audience'
+    client=ExtendedClient(client_id='client_id', grant_type='password', username='user', password='pass'), 
+    client_secret='client_secret', 
+    token_url='https://example.com/oauth/token', 
+    audience='audience'
 )
 
 call_credentials = grpc.metadata_call_credentials(oauth2_plugin)

perxis/auth.py

 import time
+from typing import Type
 
 import grpc
 
-from oauthlib.oauth2 import BackendApplicationClient, OAuth2Token
+from oauthlib.oauth2 import Client, OAuth2Token
 from requests_oauthlib import OAuth2Session
 
 
 class OAuth2Plugin(grpc.AuthMetadataPlugin):
     _token = None
 
-    def __init__(self, client_id: str, client_secret: str, token_url: str, audience: str,
+    def __init__(self, client: Type[Client], client_secret: str, token_url: str, audience: str,
                  signature_header_key: str = 'Authorization', token_type: str = 'Bearer') -> None:
 
-        self._client_id = client_id
         self._client_secret = client_secret
         self._token_url = token_url
         self._audience = audience
         self._signature_header_key = signature_header_key
         self._token_type = token_type
 
-        self.oauth2 = OAuth2Session(client=BackendApplicationClient(client_id=client_id))
+        self.oauth2 = OAuth2Session(client=client)
 
     def __call__(self, context: grpc.AuthMetadataContext,
                  callback: grpc.AuthMetadataPluginCallback) -> None:
@@ -27,17 +27,27 @@ class OAuth2Plugin(grpc.AuthMetadataPlugin):
 
     @property
     def token(self) -> OAuth2Token:
-        if self._token is None:
-            self._token = self.oauth2.fetch_token(
+        def fetch_token() -> OAuth2Token:
+            return self.oauth2.fetch_token(
+                token_url=self._token_url,
+                client_secret=self._client_secret,
+                audience=self._audience
+            )
+
+        def refresh_token() -> OAuth2Token:
+            return self.oauth2.refresh_token(
                 token_url=self._token_url,
                 client_secret=self._client_secret,
                 audience=self._audience
             )
-        else:
-            if self._token.expires_at and self._token.expires_at < time.time():
-                self._token = self.oauth2.refresh_token(
-                    token_url=self._token_url,
-                    client_secret=self._client_secret,
-                    audience=self._audience
-                )
+
+        if self._token is None:
+            self._token = fetch_token()
+
+        if self._token.expires_at and self._token.expires_at < time.time():
+            if 'refresh_token' in self._token:
+                self._token = refresh_token()
+            else:
+                self._token = fetch_token()
+
         return self._token