This wasn’t terribly easy to find, so hopefully it will help some Googler:
LWP will support https URLs if the Crypt::SSLeay module is installed.
501 Protocol scheme ‘https’ is not supported (Crypt::SSLeay not installed).
it is required that the IIS internet guest account (iusr) has
‘Read and Execute’ permissions set on the Crypt-SSLeay dlls,
namely, ssleay32.dll and libeay32.dll. to set permissions,
locate these files, choose properties from the context menu, and
under the security tab, add the iuser account to the user names menu
with ‘Read and Execute’ permissions checked.