providers/proxy: fix redirect_uri (cherry-pick #12121) (#12125)

providers/proxy: fix redirect_uri (#12121)

Signed-off-by: Jens Langhammer <jens@goauthentik.io>
Co-authored-by: Jens L. <jens@goauthentik.io>

Author: gcp-cherry-pick-bot[bot]

authentik/providers/proxy/models.py

@@ -34,10 +34,9 @@ def _get_callback_url(uri: str) -> list[RedirectURI]:
     return [
         RedirectURI(
             RedirectURIMatchingMode.STRICT,
-            urljoin(uri, "outpost.goauthentik.io/callback")
-            + f"\\?{OUTPOST_CALLBACK_SIGNATURE}=true",
+            urljoin(uri, "outpost.goauthentik.io/callback") + f"?{OUTPOST_CALLBACK_SIGNATURE}=true",
         ),
-        RedirectURI(RedirectURIMatchingMode.STRICT, uri + f"\\?{OUTPOST_CALLBACK_SIGNATURE}=true"),
+        RedirectURI(RedirectURIMatchingMode.STRICT, uri + f"?{OUTPOST_CALLBACK_SIGNATURE}=true"),
     ]