In letsencrypt/boulder#2278 we have an issue where TLDs that are IDNs are not recognized by Boulder as ending in a public suffix. Boulder currently calls publicsuffix.DefaultList.Find with the A-label form of the domain.

We have a few options:

1. Boulder could convert to U-label for querying publicsuffix
2. publicsuffix-go could switch to looking up by A-label by default
3. publicsuffix-go could offer a different set of methods for looking up by A-label.

I think (2) is my ideal solution. What do you think?