Open Redirect via "next" parameter in third-party authentication

Hi, It is currently possible to execute an open redirection attack via the `next` parameter with the inclusion of a triple-slash prefix. ## Proof of Concept ### Redirect URL ``` https://demo.weblate.org/accounts/login/github/?next=///google.com ``` After authenticating, the user will be immediately redirected to the attacker-specified target. I believe this affects all third-party authentication providers on the Weblate platform. Please let me know if you require any additional details regarding this vulnerability. Thanks!