title: how to install debian package from unsigned repository
body: <p>Trying to install Debian package to Debian 9 from unsigned repository:</p>
  
  <pre><code># apt-get --allow-unauthenticated update
  Get:1 http://files.freeswitch.org/repo/deb/freeswitch-1.8 stretch InRelease [3,196 B]
  Hit:2 http://security.debian.org/debian-security stretch/updates InRelease
  Ign:1 http://files.freeswitch.org/repo/deb/freeswitch-1.8 stretch InRelease
  Ign:3 http://debianmirror.nkn.in/debian stretch InRelease
  Hit:4 http://debianmirror.nkn.in/debian stretch Release
  Fetched 3,196 B in 1s (1,940 B/s)
  Reading package lists... Done
  W: GPG error: http://files.freeswitch.org/repo/deb/freeswitch-1.8 stretch InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY BD3189F5A2B57698
  W: The repository 'http://files.freeswitch.org/repo/deb/freeswitch-1.8 stretch InRelease' is not signed.
  N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
  N: See apt-secure(8) manpage for repository creation and user configuration details.
  </code></pre>
  
  <p>But I need it. How can I do it? Thanx!</p>