feat: provide way to configure default strategy

This is to provide app modules way to provide default strategy for the
backends. Django app currently handles this by monkey-patching the
constructor in baseauth_init_workaround.

Fixes #1490

Author: nijel

social_core/backends/base.py

@@ -7,6 +7,8 @@
 import requests
 
 from social_core.exceptions import AuthConnectionError, AuthUnknownError
+from social_core.registry import REGISTRY
+from social_core.storage import UserProtocol
 from social_core.utils import module_member, parse_qs, social_logger, user_agent
 
 if TYPE_CHECKING:
@@ -31,8 +33,11 @@ class BaseAuth:
     REQUIRES_EMAIL_VALIDATION = False
     SEND_USER_AGENT = True
 
-    def __init__(self, strategy, redirect_uri=None) -> None:
-        self.strategy = strategy
+    def __init__(self, strategy=None, redirect_uri: str | None = None) -> None:
+        # TODO: temporary type override
+        self.strategy: Any = (
+            strategy if strategy is not None else REGISTRY.default_strategy
+        )
         self.redirect_uri = redirect_uri
         self.data = self.strategy.request_data()
         self.redirect_uri = self.strategy.absolute_uri(self.redirect_uri)

social_core/backends/open_id_connect.py

@@ -7,6 +7,8 @@
 from typing import TYPE_CHECKING, Any, Literal
 
 import jwt
+from cryptography.hazmat.backends import default_backend
+from cryptography.hazmat.primitives import hashes
 from jwt import (
     ExpiredSignatureError,
     InvalidAudienceError,
@@ -28,9 +30,6 @@
 
     from requests.auth import AuthBase
 
-from cryptography.hazmat.backends import default_backend
-from cryptography.hazmat.primitives import hashes
-
 
 class OpenIdConnectAssociation:
     """Use Association model to save the nonce by force."""
@@ -88,7 +87,7 @@ class OpenIdConnectAuth(BaseOAuth2):
     LOGIN_HINT = None
     ACR_VALUES = None
 
-    def __init__(self, strategy, redirect_uri=None) -> None:
+    def __init__(self, strategy=None, redirect_uri: str | None = None) -> None:
         super().__init__(strategy, redirect_uri=redirect_uri)
         self.id_token = None
 

social_core/exceptions.py

@@ -22,6 +22,13 @@ def __str__(self) -> str:
         return f"Strategy {self.strategy_name} does not support {self.feature_name}"
 
 
+class DefaultStrategyMissingError(SocialAuthBaseException):
+    """Default strategy is not configured."""
+
+    def __str__(self) -> str:
+        return "Default strategy is not configured"
+
+
 class StrategyMissingBackendError(SocialAuthBaseException):
     """Strategy storage backend is not configured."""
 

social_core/registry.py

@@ -0,0 +1,29 @@
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
+from .exceptions import DefaultStrategyMissingError
+
+if TYPE_CHECKING:
+    from .strategy import BaseStrategy
+
+
+class Registry:
+    def __init__(self) -> None:
+        self._default_strategy: BaseStrategy | None = None
+
+    def reset(self) -> None:
+        self._default_strategy = None
+
+    @property
+    def default_strategy(self) -> BaseStrategy:
+        if self._default_strategy is None:
+            raise DefaultStrategyMissingError
+        return self._default_strategy
+
+    @default_strategy.setter
+    def default_strategy(self, strategy: BaseStrategy) -> None:
+        self._default_strategy = strategy
+
+
+REGISTRY = Registry()

social_core/tests/test_registry.py

@@ -0,0 +1,21 @@
+import unittest
+
+from social_core.exceptions import (
+    DefaultStrategyMissingError,
+)
+from social_core.registry import REGISTRY
+
+from .strategy import TestStrategy
+
+
+class StrategyRegistryTestCase(unittest.TestCase):
+    def test_missing(self):
+        with self.assertRaises(DefaultStrategyMissingError):
+            self.assertIsNotNone(REGISTRY.default_strategy)
+
+    def test_set(self):
+        REGISTRY.default_strategy = TestStrategy(None)
+        try:
+            self.assertIsInstance(REGISTRY.default_strategy, TestStrategy)
+        finally:
+            REGISTRY.reset()