Refa: make RAGFlow more asynchronous (#11601)

### What problem does this PR solve?

Try to make this more asynchronous. Verified in chat and agent
scenarios, reducing blocking behavior. #11551, #11579.

However, the impact of these changes still requires further
investigation to ensure everything works as expected.

### Type of change

- [x] Refactoring

api/apps/auth/oauth.py

@@ -14,8 +14,8 @@
 #  limitations under the License.
 #
 
-import requests
 import urllib.parse
+from common.http_client import async_request, sync_request
 
 
 class UserInfo:
@@ -74,15 +74,40 @@ class OAuthClient:
                 "redirect_uri": self.redirect_uri,
                 "grant_type": "authorization_code"
             }
-            response = requests.post(
+            response = sync_request(
+                "POST",
                 self.token_url,
                 data=payload,
                 headers={"Accept": "application/json"},
-                timeout=self.http_request_timeout
+                timeout=self.http_request_timeout,
             )
             response.raise_for_status()
             return response.json()
-        except requests.exceptions.RequestException as e:
+        except Exception as e:
+            raise ValueError(f"Failed to exchange authorization code for token: {e}")
+
+    async def async_exchange_code_for_token(self, code):
+        """
+        Async variant of exchange_code_for_token using httpx.
+        """
+        payload = {
+            "client_id": self.client_id,
+            "client_secret": self.client_secret,
+            "code": code,
+            "redirect_uri": self.redirect_uri,
+            "grant_type": "authorization_code",
+        }
+        try:
+            response = await async_request(
+                "POST",
+                self.token_url,
+                data=payload,
+                headers={"Accept": "application/json"},
+                timeout=self.http_request_timeout,
+            )
+            response.raise_for_status()
+            return response.json()
+        except Exception as e:
             raise ValueError(f"Failed to exchange authorization code for token: {e}")
 
 
@@ -92,11 +117,27 @@ class OAuthClient:
         """
         try:
             headers = {"Authorization": f"Bearer {access_token}"}
-            response = requests.get(self.userinfo_url, headers=headers, timeout=self.http_request_timeout)
+            response = sync_request("GET", self.userinfo_url, headers=headers, timeout=self.http_request_timeout)
             response.raise_for_status()
             user_info = response.json()
             return self.normalize_user_info(user_info)
-        except requests.exceptions.RequestException as e:
+        except Exception as e:
+            raise ValueError(f"Failed to fetch user info: {e}")
+
+    async def async_fetch_user_info(self, access_token, **kwargs):
+        """Async variant of fetch_user_info using httpx."""
+        headers = {"Authorization": f"Bearer {access_token}"}
+        try:
+            response = await async_request(
+                "GET",
+                self.userinfo_url,
+                headers=headers,
+                timeout=self.http_request_timeout,
+            )
+            response.raise_for_status()
+            user_info = response.json()
+            return self.normalize_user_info(user_info)
+        except Exception as e:
             raise ValueError(f"Failed to fetch user info: {e}")