The online repository with latest Squid 4.9 (rebuilt from Debian unstable with sslbump support) for Ubuntu 18 LTS 64-bit is available at squid49.diladele.com.
Github repo at
https://github.com/diladele/squid-ubuntu contains the scripts we used to make this compilation.
Scripts for Ubuntu 16 are also available in that repo.
Hope you will find this helpful. Note that older repo of squid48.diladele.com will be taken down in 1 year.
P.S. Here are simple instructions how to use the repo. For more information see readme at
# add diladele apt key
wget -qO -
http://packages.diladele.com/diladele_pub.asc | sudo apt-key add -
# add repo
http://squid49.diladele.com/ubuntu/ bionic main" > /etc/apt/sources.list.d/squid49.diladele.com.list
# update the apt cache
apt-get install squid-common
apt-get install squid
apt-get install squidclient
Please take a look at another our project – DNS Safety filtering server. Sort of Web Safety implemented as DNS Server. Might be interesting in deployments where HTTPS decryption is not possible.