There were unauthenticated packages and -y was used without --allow-unauthenticated

[MiteshShah]

OS: Ubuntu 16.04

vim /etc/apt/sources.list.d/nginx.list
deb http://download.opensuse.org/repositories/home:/rtCamp:/EasyEngine/xUbuntu_16.04/ /

 curl http://download.opensuse.org/repositories/home:/rtCamp:/EasyEngine/xUbuntu_16.04/Release.key | sudo apt-key add -
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100  1094  100  1094    0     0  16450      0 --:--:-- --:--:-- --:--:-- 16575
OK

 apt-get update
Hit:1 http://archive.ubuntu.com/ubuntu xenial InRelease
Ign:2 http://download.opensuse.org/repositories/home:/rtCamp:/EasyEngine/xUbuntu_16.04  InRelease
Hit:3 http://archive.ubuntu.com/ubuntu xenial-updates InRelease     
Hit:4 http://download.opensuse.org/repositories/home:/rtCamp:/EasyEngine/xUbuntu_16.04  Release
Get:5 http://download.opensuse.org/repositories/home:/rtCamp:/EasyEngine/xUbuntu_16.04  Release.gpg [481 B]
Hit:6 http://security.ubuntu.com/ubuntu xenial-security InRelease              
Hit:7 http://archive.ubuntu.com/ubuntu xenial-backports InRelease          
Fetched 481 B in 0s (529 B/s)                        
Reading package lists... Done

apt-get install -y nginx-custom
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following additional packages will be installed:
  fontconfig-config fonts-dejavu-core libfontconfig1 libgd3 libjbig0 libjpeg-turbo8 libjpeg8 libluajit-5.1-2 libluajit-5.1-common libssl1.0.2 libtiff5
  libvpx3 libxpm4 libxslt1.1 nginx-ee
Suggested packages:
  libgd-tools nginx-doc fcgiwrap ssl-cert
The following NEW packages will be installed:
  fontconfig-config fonts-dejavu-core libfontconfig1 libgd3 libjbig0 libjpeg-turbo8 libjpeg8 libluajit-5.1-2 libluajit-5.1-common libssl1.0.2 libtiff5
  libvpx3 libxpm4 libxslt1.1 nginx-custom nginx-ee
0 upgraded, 16 newly installed, 0 to remove and 10 not upgraded.
Need to get 4,760 kB of archives.
After this operation, 14.5 MB of additional disk space will be used.
WARNING: The following packages cannot be authenticated!
  libssl1.0.2 nginx-ee nginx-custom
E: There were unauthenticated packages and -y was used without --allow-unauthenticated

[MiteshShah]

@rahul286 @iam404 Possible fix

$ cd /var/lib/apt/lists/
$ ls download.opensuse.org_repositories_home\:_rtCamp\:_EasyEngine_xUbuntu%5f16.04_*
download.opensuse.org_repositories_home:_rtCamp:_EasyEngine_xUbuntu%5f16.04_Packages
download.opensuse.org_repositories_home:_rtCamp:_EasyEngine_xUbuntu%5f16.04_Release

$ rm -rf /var/lib/apt/lists/*
$ apt-get update

$ ls download.opensuse.org_repositories_home\:_rtCamp\:_EasyEngine_xUbuntu%5f16.04_*
download.opensuse.org_repositories_home:_rtCamp:_EasyEngine_xUbuntu%5f16.04_Packages
download.opensuse.org_repositories_home:_rtCamp:_EasyEngine_xUbuntu%5f16.04_Release
download.opensuse.org_repositories_home:_rtCamp:_EasyEngine_xUbuntu%5f16.04_Release.gpg

If you notice the download.opensuse.org_repositories_home:_rtCamp:_EasyEngine_xUbuntu%5f16.04_Release.gpg now added which will fix my issue to directly use rtcamp nginx build.

I'm not sure why its cause the problem at first time
I'd tried many times on vagrant and each time I'd to remove the list and update the package to fix the issue.