We want to copy the backups automatically via WebDav. Unfortunately this fails. Our WebDav access uses certificates from our own certification authority.
Therefore it would be nice if the certification authority could be added or activated in UpdraftPlus. The generated certificates can be verified via the Internet.
Due to a company policy, only own certificates should be used for certain accesses such as this one.
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This idea was posted in UpdraftPlus - backup/restore plugin and tagged backup, certificate, certificate-authority, storage, webdav on August 6, 2019 by 
Andreas Reisenhofer.
The WebDAV module uses PHP functions for network operations, and thus the SSL certificates used are those configured in your PHP install.
Thank you for your answer. That is strange, because PHP accept that certificate, but not UpdraftPlus. According to the feedback, I will investigate the matter further.
best regards, Andreas