auth: add client_creds_dict

This allows programmatic use without having to create a temporary file.

Author: efiop

pydrive2/auth.py

@@ -303,7 +303,14 @@ def ServiceAuth(self):
             self.LoadServiceConfigSettings()
         scopes = scopes_to_string(self.settings["oauth_scope"])
         client_service_json = self.client_config.get("client_json_file_path")
-        if client_service_json:
+        creds_dict = self.client_config.get("client_creds_dict")
+        if creds_dict:
+            self.credentials = (
+                ServiceAccountCredentials.from_json_keyfile_dict(
+                    keyfile_dict=creds_dict, scopes=scopes
+                )
+            )
+        elif client_service_json:
             self.credentials = (
                 ServiceAccountCredentials.from_json_keyfile_name(
                     filename=client_service_json, scopes=scopes