mod_auth_mellon through 0.14.2 has an Open Redirect via the login?ReturnTo= substring, as demonstrated by omitting the // after http: in the target URL.
https://www.oracle.com/security-alerts/cpuapr2022.html
https://usn.ubuntu.com/4291-1/
https://lists.debian.org/debian-lts-announce/2023/03/msg00010.html
https://github.com/Uninett/mod_auth_mellon/issues/35#issuecomment-503974885