Revert "chore: remove unused _AuthStore class and related imports"

This reverts commit 3f066f2b0f.

lib/crewai/src/crewai/a2a/auth/utils.py

@@ -6,7 +6,9 @@ OAuth2, API keys, and HTTP authentication methods.
 
 import asyncio
 from collections.abc import Awaitable, Callable, MutableMapping
+import hashlib
 import re
+import threading
 from typing import Final, Literal, cast
 
 from a2a.client.errors import A2AClientHTTPError
@@ -29,6 +31,40 @@ from crewai.a2a.auth.client_schemes import (
 )
 
 
+class _AuthStore:
+    """Store for authentication schemes with safe concurrent access."""
+
+    def __init__(self) -> None:
+        self._store: dict[str, ClientAuthScheme | None] = {}
+        self._lock = threading.RLock()
+
+    @staticmethod
+    def compute_key(auth_type: str, auth_data: str) -> str:
+        """Compute a collision-resistant key using SHA-256."""
+        content = f"{auth_type}:{auth_data}"
+        return hashlib.sha256(content.encode()).hexdigest()
+
+    def set(self, key: str, auth: ClientAuthScheme | None) -> None:
+        """Store an auth scheme."""
+        with self._lock:
+            self._store[key] = auth
+
+    def get(self, key: str) -> ClientAuthScheme | None:
+        """Retrieve an auth scheme by key."""
+        with self._lock:
+            return self._store.get(key)
+
+    def __setitem__(self, key: str, value: ClientAuthScheme | None) -> None:
+        with self._lock:
+            self._store[key] = value
+
+    def __getitem__(self, key: str) -> ClientAuthScheme | None:
+        with self._lock:
+            return self._store[key]
+
+
+_auth_store = _AuthStore()
+
 _SCHEME_PATTERN: Final[re.Pattern[str]] = re.compile(r"(\w+)\s+(.+?)(?=,\s*\w+\s+|$)")
 _PARAM_PATTERN: Final[re.Pattern[str]] = re.compile(r'(\w+)=(?:"([^"]*)"|([^\s,]+))')