'Not a Certification Authority' while importing self-signed certificate

Just to make sure we're covering our bases... Have you tried the processes outlined here? https://stackoverflow.com/questions/7580508/getting-chrome-to-accept-self-signed-localhost-certificate

That used to work for me, but as of this morning, after updating to Chrome 58.0.3029.81, I also get the following error in the console for a self-signed cert that used to work on Ubuntu 16.04:

Certificate Error
There are issues with the site's certificate chain (net::ERR_CERT_AUTHORITY_INVALID).

EDIT:

I've just had success with one of the methods from the link I referenced above. It completely goes around Chrome because it seems like something has changed with Chrome and it's not working right anymore.

To dump the cert using OpenSSL client (probably not necessary, but in case you want to be very thorough):

$ echo QUIT | openssl s_client -connect $DOMAIN_TO_FETCH_FROM:443 | sed -ne '/BEGIN CERT/,/END CERT/p' > my-cert

To install the dumped cert using certutil. If you didn't dump your cert with openssl, replace my-cert with whatever filename is appropriate:

$ certutil -d sql:$HOME/.pki/nssdb -A -t "P,," -n my-cert -i my-cert

Check the installation of the cert with certutil (if you feel so inclined):

$ certutil -d sql:$HOME/.pki/nssdb -L

# Certificate Nickname                                         Trust Attributes
#                                                              SSL,S/MIME,JAR/XPI
#
# my-cert                                                      P,,  

Completely close and restart Chrome, and maybe you will find success. Worked for me on both 58 and 59-beta.