feat(storage): add async credential wrapper

Author: googlyrahman

google/cloud/storage/_experimental/asyncio/async_creds.py

@@ -0,0 +1,36 @@
+"""Async Wrapper around Google Auth Credentials"""
+
+import asyncio
+from google.auth.aio import credentials as async_creds
+from google.auth.transport.requests import Request
+
+class AsyncCredsWrapper(async_creds.Credentials):
+    """Wraps synchronous Google Auth credentials to provide an asynchronous interface.
+
+    This class adapts standard synchronous `google.auth.credentials.Credentials` for use 
+    in asynchronous contexts. It offloads blocking operations, such as token refreshes, 
+    to a separate thread using `asyncio.loop.run_in_executor`.
+
+    Args:
+        sync_creds (google.auth.credentials.Credentials): The synchronous credentials 
+            instance to wrap.
+    """
+
+    def __init__(self, sync_creds):
+        super().__init__()
+        self.creds = sync_creds
+        self._loop = asyncio.get_event_loop()
+
+    async def refresh(self, _request):
+        await self._loop.run_in_executor(
+            None, self.creds.refresh, Request()
+        )
+
+    async def before_request(self, _request, method, url, headers):
+        if self.creds.valid:
+            self.creds.apply(headers)
+            return
+
+        await self._loop.run_in_executor(
+            None, self.creds.before_request, Request(), method, url, headers
+        )