Handle URLs from Starlette's url_for() method which post 0.26.0 retur…

…ns a URL instance and not a string

authlib/integrations/starlette_client/apps.py

@@ -1,3 +1,4 @@
+from starlette.datastructures import URL
 from starlette.responses import RedirectResponse
 from ..base_client import OAuthError
 from ..base_client import BaseApp
@@ -26,6 +27,10 @@ async def authorize_redirect(self, request, redirect_uri=None, **kwargs):
         :param kwargs: Extra parameters to include.
         :return: A HTTP redirect response.
         """
+
+        # Handle Starlette >= 0.26.0 where redirect_uri may now be a URL and not a string
+        if redirect_uri and isinstance(redirect_uri, URL):
+            redirect_uri = str(redirect_uri)
         rv = await self.create_authorization_url(redirect_uri, **kwargs)
         await self.save_authorize_data(request, redirect_uri=redirect_uri, **rv)
         return RedirectResponse(rv['url'], status_code=302)