Unable to install aptly on Ubuntu 16.04

[geetotes]

When I try to use this module, I get the following error when running puppet apply:

Error: Execution of '/usr/bin/apt-get -q -y -o DPkg::Options::=--force-confold install aptly' returned 100: Reading package lists...
Building dependency tree...
Reading state information...
The following NEW packages will be installed:
  aptly
0 upgraded, 1 newly installed, 0 to remove and 62 not upgraded.
Need to get 6420 kB of archives.
After this operation, 22.6 MB of additional disk space will be used.
WARNING: The following packages cannot be authenticated!
  aptly
E: There were unauthenticated packages and -y was used without --allow-unauthenticated
Error: /Stage[main]/Aptly::Install/Package[aptly]/ensure: change from purged to present failed: Execution of '/usr/bin/apt-get -q -y -o DPkg::Options::=--force-confold install aptly' returned 100: Reading package lists...
Building dependency tree...
Reading state information...
The following NEW packages will be installed:
  aptly
0 upgraded, 1 newly installed, 0 to remove and 62 not upgraded.
Need to get 6420 kB of archives.
After this operation, 22.6 MB of additional disk space will be used.
WARNING: The following packages cannot be authenticated!
  aptly
E: There were unauthenticated packages and -y was used without --allow-unauthenticated

It's like apt-get update isn't getting run? I'm not sure why this is happening. My manifest is copy-pasta'd from the readme:

class aptly-config() {
  class { 'aptly':
    root_dir      => '/mirror',
    architectures => ['amd64']
  }

  aptly::mirror { 'debian_stable':
    location      => 'http://ftp.us.debian.org/debian/',
    distribution  => 'stable',
    components    => [ 'main'] ,
    architectures => ['amd64'],
  }

  exec { 'debian_stable_key_8B48AD6246925553':
    command => '/usr/bin/gpg --no-default-keyring --keyring trustedkeys.gpg --keyserver keys.gnupg.net --recv-key 8B48AD6246925553',
    unless  => '/usr/bin/gpg --no-default-keyring --keyring trustedkeys.gpg --list-key 8B48AD6246925553 > /dev/null 2>&1',
  }

  exec { 'debian_stable_key_7638D0442B90D010':
    command => '/usr/bin/gpg --no-default-keyring --keyring trustedkeys.gpg --keyserver keys.gnupg.net --recv-key 7638D0442B90D010',
    unless  => '/usr/bin/gpg --no-default-keyring --keyring trustedkeys.gpg --list-key 7638D0442B90D010 > /dev/null 2>&1',
  }

  exec { 'debian_stable_key_CBF8D6FD518E17E1':
    command => '/usr/bin/gpg --no-default-keyring --keyring trustedkeys.gpg --keyserver keys.gnupg.net --recv-key CBF8D6FD518E17E1',
    unless  => '/usr/bin/gpg --no-default-keyring --keyring trustedkeys.gpg --list-key CBF8D6FD518E17E1 > /dev/null 2>&1',
  }


  Exec['debian_stable_key_8B48AD6246925553']->
  Exec['debian_stable_key_7638D0442B90D010']->
  Exec['debian_stable_key_CBF8D6FD518E17E1']->
  Aptly::Mirror['debian_stable']

}

[geetotes]

I've been able to install aptly by modifying the install options in manifests/install.pp

    'Debian': {
      Package {
        provider => 'apt',
        install_options => '--allow-unauthenticated'
      }
    }

I am using Apt version 2.4

[morremeyer]

The key that aptly is signed with has been changed and is outdated, try to use the key with the ID 26DA9D8630302E0B86A7A2CBED75B5A4483DA07C.