"How would you implement a secure login field on a high traffic website where performance is a consideration?"
....
"wanting to serve the front page in HTTP, while needing to present the login form via HTTPs"
Maybe. There will still be a link on the HTTP page that takes you to a HTTPS page with a login form. Someone with MITM access could alter that link. A better way would be to serve all pages via HTTPS
Maybe. There will still be a link on the HTTP page that takes you to a HTTPS page with a login form. Someone with MITM access could alter that link. A better way would be to serve all pages via HTTPS