GHSA-F59H-Q822-G45G Caddy: FastCGI header normalization bypass in `forward_auth copy_headers`

Summary forwardauth copyheaders deletes the exact client-supplied identity header before copying the trusted value from the auth gateway. But when the request later goes through phpfastcgi, Caddy normalizes HTTP headers into CGI variables by replacing - with . This lets a client send an underscor...