The original Keepass2 client allows you to use webdav as storage backend for the keepass file where all the passwords are stored. however, it seems to be a bit tricky to get https to work with keepass2 under linux (ubuntu in my case).
there are different options which one can try:
Options → Advanced → File Input/Output Connections → Accept invalid SSL certificates
sudo apt-get install mono-devel sudo mozroots --import --sync --machine #if you see an error that it could not download the file, copy/paste the url into your webbrowser. it will redirect to a new url, copy/paste that url to the --url option of the command: sudo mozroots --import --sync --machine --url "https://hg.mozilla.org/mozilla-central/raw-file/tip/security/nss/lib/ckfw/builtins/certdata.txt"
unfortunately this did not work for me but some stated it worked.. maybe a reload of some sorts is necessary after that..
ca-certificates-monopackage, but this seems to only be availble starting ubuntu 16.04 which i haven't been able to test yet.