trust server certificate with lftp
Solution 1:
The only solution a year later is still to turn off ssl:verify-certificate for specific certificate fingerprints.
set ssl:verify-certificate/{fingerprint1} no
set ssl:verify-certificate/{fingerprint2} no
See lftp closed issue 214 -- https://github.com/lavv17/lftp/issues/214#issuecomment-197237482