Need to force deb install (--force-yes)

In folsom install doc : http://docs.openstack.org/folsom/basic-install/content/basic-install_controller.html
We need to install some packages : "apt-get -y install glance glance-api python-glanceclient glance-common"

But there is an error if we don't use --force-yes parameter :

root@ip-10-130-153-26:~# apt-get -y install glance glance-api python-glanceclient glance-common
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following extra packages will be installed:
  glance-registry libjs-sphinxdoc libjs-underscore libxslt1.1 python-amqplib python-anyjson python-dateutil python-decorator
  python-eventlet python-formencode python-gevent python-glance python-greenlet python-iso8601 python-jsonschema python-keystone
  python-keystoneclient python-kombu python-lxml python-migrate python-openid python-passlib python-paste python-pastedeploy
  python-pastescript python-prettytable python-requests python-routes python-scgi python-sqlalchemy python-sqlalchemy-ext
  python-swiftclient python-tempita python-warlock python-webob python-xattr
Suggested packages:
  python-ceph javascript-common python-amqplib-doc python-egenix-mxdatetime python-dns python-gevent-doc python-gevent-dbg
  python-greenlet-dbg python-greenlet-dev python-greenlet-doc python-memcache python-couchdb python-kombu-doc python-pymongo
  python-lxml-dbg python-pastewebkit libapache2-mod-wsgi libapache2-mod-python libapache2-mod-scgi python-pgsql libjs-mochikit python-flup
  python-cherrypy python-sqlalchemy-doc python-psycopg2 python-mysqldb python-kinterbasdb python-pymssql
The following NEW packages will be installed:
  glance glance-api glance-common glance-registry libjs-sphinxdoc libjs-underscore libxslt1.1 python-amqplib python-anyjson
  python-dateutil python-decorator python-eventlet python-formencode python-gevent python-glance python-glanceclient python-greenlet
  python-iso8601 python-jsonschema python-keystone python-keystoneclient python-kombu python-lxml python-migrate python-openid
  python-passlib python-paste python-pastedeploy python-pastescript python-prettytable python-requests python-routes python-scgi
  python-sqlalchemy python-sqlalchemy-ext python-swiftclient python-tempita python-warlock python-webob python-xattr
0 upgraded, 40 newly installed, 0 to remove and 2 not upgraded.
Need to get 4,061 kB of archives.
After this operation, 22.3 MB of additional disk space will be used.
WARNING: The following packages cannot be authenticated!
  python-greenlet python-eventlet python-jsonschema python-sqlalchemy python-prettytable python-sqlalchemy-ext python-warlock
  python-keystoneclient python-keystone python-swiftclient python-glance glance-common glance-api glance-registry glance
  python-glanceclient
E: There are problems and -y was used without --force-yes
root@ip-10-130-153-26:~#

And that's a problem, especially because I'd like to install these paquages via a template (--force-yes does not exist).

A workaround for ignoring errors : echo 'APT::Get::AllowUnauthenticated "true";' >> /etc/apt/apt.conf.d/70debconf