This depends how you pronounce 'h'. If you pronounce it "aitch", then "an HTTPS" is correct. If you pronounce it "haitch", then "a HTTPS" is correct. There's no

This depends how you pronounce 'h'. If you pronounce it "aitch", then "an HTTPS" is correct. If you pronounce it "haitch", then "a HTTPS" is correct. There's no universal pronunciation, and therefore no universally-right answer.