HSTS bypass via IDN

curl’s HSTS check could be bypassed to trick it to keep using HTTP.

Using its HSTS support, curl can be instructed to use HTTPS directly instead
of using an insecure clear-text HTTP step even when HTTP is provided in the
URL. This mechanism could be bypassed if the hostname in the given URL uses
IDN characters that get replaced to ASCII counterparts as part of the IDN
conversion. Like using the character UTF-8 U+3002 (IDEOGRAPHIC FULL STOP)
instead of the common ASCII full stop (U+002E) ..

Like this: http://curl。se。