Cargo can be coerced to share credentials between registries

Cargo between 1.68 and 1.96 incorrectly normalized the URLs of third-party registries using the sparse index protocol. If a hosting provider allowed multiple registries to be hosted with arbitrary names within the same domain, an attacker able to publish crates in a registry could obtain the credentials of others users of the same registry. The severity of the vulnerability is **low**, due to the extremely niche requirements needed to achieve the attack.