Add Key file such as this:
wget -O- https://duo.com/DUO-GPG-PUBLIC-KEY.asc |
gpg --dearmor |
tee /etc/apt/keyrings/duo.gpg
Add new file to sources.list.d with content referencing the new key:
deb [signed-by=/etc/apt/keyrings/duo.gpg] https://pkg.duosecurity.com/Debian bullseye main
Update and install application:
apt update
apt install duo-unix