Install needed packages:
sudo dnf install qt5-qtbase-devel openssl-devel qtkeychain-qt5-devel -y
# create a symlink to /usr/bin/qmake, if needed
sudo ln -s /usr/lib64/qt5/bin/qmake /usr/bin/qmake
cd ~/tools
git clone https://github.com/theinvisible/openfortigui.git
cd openfortigui && git submodule init && git submodule update
qmake && make -j4
# install it as an application
sudo cp openfortigui/app-entry/openfortigui.png /usr/share/pixmaps
sudo cp openfortigui/app-entry/openfortigui.desktop /usr/share/applications
sudo cp openfortigui/openfortigui /usr/bin/