diff --git a/authlib/integrations/httpx_client/assertion_client.py b/authlib/integrations/httpx_client/assertion_client.py
index 83dc58b2..dfe9d96e 100644
--- a/authlib/integrations/httpx_client/assertion_client.py
+++ b/authlib/integrations/httpx_client/assertion_client.py
@@ -22,6 +22,11 @@ def __init__(self, token_endpoint, issuer, subject, audience=None, grant_type=No
                  claims=None, token_placement='header', scope=None, **kwargs):
 
         client_kwargs = extract_client_kwargs(kwargs)
+        # app keyword was dropped!
+        app_value = client_kwargs.pop('app', None)
+        if app_value is not None:
+            client_kwargs['transport'] = httpx.ASGITransport(app=app_value)
+
         httpx.AsyncClient.__init__(self, **client_kwargs)
 
         _AssertionClient.__init__(
@@ -61,6 +66,11 @@ def __init__(self, token_endpoint, issuer, subject, audience=None, grant_type=No
                  claims=None, token_placement='header', scope=None, **kwargs):
 
         client_kwargs = extract_client_kwargs(kwargs)
+        # app keyword was dropped!
+        app_value = client_kwargs.pop('app', None)
+        if app_value is not None:
+            client_kwargs['transport'] = httpx.WSGITransport(app=app_value)
+
         httpx.Client.__init__(self, **client_kwargs)
 
         _AssertionClient.__init__(
diff --git a/authlib/integrations/httpx_client/oauth1_client.py b/authlib/integrations/httpx_client/oauth1_client.py
index ce031c97..f4862a14 100644
--- a/authlib/integrations/httpx_client/oauth1_client.py
+++ b/authlib/integrations/httpx_client/oauth1_client.py
@@ -34,6 +34,11 @@ def __init__(self, client_id, client_secret=None,
                  force_include_body=False, **kwargs):
 
         _client_kwargs = extract_client_kwargs(kwargs)
+        # app keyword was dropped!
+        app_value = _client_kwargs.pop('app', None)
+        if app_value is not None:
+            _client_kwargs['transport'] = httpx.ASGITransport(app=app_value)
+
         httpx.AsyncClient.__init__(self, **_client_kwargs)
 
         _OAuth1Client.__init__(
@@ -87,6 +92,11 @@ def __init__(self, client_id, client_secret=None,
                  force_include_body=False, **kwargs):
 
         _client_kwargs = extract_client_kwargs(kwargs)
+        # app keyword was dropped!
+        app_value = _client_kwargs.pop('app', None)
+        if app_value is not None:
+            _client_kwargs['transport'] = httpx.WSGITransport(app=app_value)
+
         httpx.Client.__init__(self, **_client_kwargs)
 
         _OAuth1Client.__init__(
diff --git a/authlib/integrations/httpx_client/oauth2_client.py b/authlib/integrations/httpx_client/oauth2_client.py
index 5b2d3fdd..16dea88d 100644
--- a/authlib/integrations/httpx_client/oauth2_client.py
+++ b/authlib/integrations/httpx_client/oauth2_client.py
@@ -62,6 +62,11 @@ def __init__(self, client_id=None, client_secret=None,
 
         # extract httpx.Client kwargs
         client_kwargs = self._extract_session_request_params(kwargs)
+        # app keyword was dropped!
+        app_value = client_kwargs.pop('app', None)
+        if app_value is not None:
+            client_kwargs['transport'] = httpx.ASGITransport(app=app_value)
+
         httpx.AsyncClient.__init__(self, **client_kwargs)
 
         # We use a Lock to synchronize coroutines to prevent
@@ -177,6 +182,11 @@ def __init__(self, client_id=None, client_secret=None,
 
         # extract httpx.Client kwargs
         client_kwargs = self._extract_session_request_params(kwargs)
+        # app keyword was dropped!
+        app_value = client_kwargs.pop('app', None)
+        if app_value is not None:
+            client_kwargs['transport'] = httpx.WSGITransport(app=app_value)
+
         httpx.Client.__init__(self, **client_kwargs)
 
         _OAuth2Client.__init__(
diff --git a/tests/clients/test_httpx/test_async_oauth2_client.py b/tests/clients/test_httpx/test_async_oauth2_client.py
index 40fb363b..8f29b973 100644
--- a/tests/clients/test_httpx/test_async_oauth2_client.py
+++ b/tests/clients/test_httpx/test_async_oauth2_client.py
@@ -4,7 +4,7 @@
 from unittest import mock
 from copy import deepcopy
 
-from httpx import AsyncClient
+from httpx import AsyncClient, ASGITransport
 
 from authlib.common.security import generate_token
 from authlib.common.urls import url_encode
@@ -96,7 +96,7 @@ async def test_add_token_to_streaming_request(assert_func, token_placement):
         token_placement="header",
         app=AsyncMockDispatch({'a': 'a'}, assert_func=assert_token_in_header)
     ),
-    AsyncClient(app=AsyncMockDispatch({'a': 'a'}))
+    AsyncClient(transport=ASGITransport(app=AsyncMockDispatch({'a': 'a'})))
 ])
 async def test_httpx_client_stream_match(client):
     async with client as client_entered: