after some testing, I find the following command works:
$ curl -g -6 'http://[fe80::3ad1:35ff:fe08:cd%eth0]:80/'
interface ‘eth0’ is the interface with ipv6 enabled, so you may need to replace it with something else.
and just in case, the telnet command to test ipv6:
$ telnet -6 fe80::3ad1:35ff:fe08:cd%eth0 80