I use three different VPN connections in my laptop: OpenConnect, OpenVPN and PPTP. I like these connections to be managed by NetworkManager and not by third parties
The first one (OpenConnect) is compatible with Cisco AnyConnect: http://www.infradead.org/openconnect/
The second one (OpenVPN) is compatible with pfSense: https://openvpn.net/
The third one is used to connect to a Point-to-Point Windows server: http://pptpclient.sourceforge.net/
After some updates in Slackware-current and KDE5, the connections stopped working. These are the steps I followed to have the connections up and running
I repackaged openconnect from https://www.slackbuilds.org/repository/14.2/network/openconnect/ and used the same NetworkManager-openconnect package for 14.2 from https://www.slackbuilds.org/repository/14.2/network/NetworkManager-openconnect/
I also found a Plasma 5 NetworkManager package at https://github.com/philipvdh/slackbuilds/tree/master/plasma5-nm-openconnect (from rworkman) by searching on Google for plasma5-nm-openconnect and followed the .info file in there to download the latest version of the package from https://github.com/KDE/plasma-nm/releases which matched with the Plasma packages (5.12.4). This last step did the trick for OpenConnect
The alternative would be to download and run the Cisco AnyConnect native client for Linux
I repackaged openvpn from https://ftp.osuosl.org/pub/slackware/slackware64-current/source/n/openvpn/ and used the NetworkManager-openvpn SlackBuilds script from https://www.slackbuilds.org/repository/14.2/network/NetworkManager-openvpn/ which worked fine, but I changed the tar.xz file to be the latest (1.8.2) and used the package from https://download.gnome.org/sources/NetworkManager-openvpn/1.8/NetworkManager-openvpn-1.8.2.tar.xz
The plasma5-nm-5.12.4 package from alienBOB worked perfectly for this connection
I imported the ovpn file that I have saved and used before
I repackaged pptp from https://www.slackbuilds.org/repository/14.2/network/pptp/using the latest version (1.10.0) from https://sourceforge.net/projects/pptpclient/files/ and used the NetworkManager-pptp SlackBuilds script from https://www.slackbuilds.org/repository/14.2/network/NetworkManager-pptp/ which worked fine, but I changed the tar.xz file to be the latest (1.2.6) and used the package from http://ftp.gnome.org/pub/GNOME/sources/NetworkManager-pptp/1.2/NetworkManager-pptp-1.2.6.tar.xz
The main part is to click on "Advanced..." and select only "MSCHAP" and "MSCHAPv2" under "Allow following authentication methods:" and "Use MPPE Encryption" with "Crypto: Any"
F. Bobbio C.