It's not that you've created another login that's the issue, but that you've provided access to secure data through an insecure mechanism. If your worried about password sniffing, what's to stop someone sniffing the password from the URL and then accessing that data when they like. And does that login allow access to other data that you weren't planning on. Or could an admin inadvertantly give that user greater rights than you planned because they don't understand the implications. Anything that circumvents the normal security model seems to me like asking for trouble.
It's not that you've created another login that's the issue, but that you've provided access to secure data through an insecure mechanism. If your worried about password sniffing, what's to stop someone sniffing the password from the URL and then accessing that data when they like. And does that login allow access to other data that you weren't planning on. Or could an admin inadvertantly give that user greater rights than you planned because they don't understand the implications. Anything that circumvents the normal security model seems to me like asking for trouble.