A very simple Puppet example of setting the authorized_keys, id_rsa, and sudoers file for passwordless sudo access.

site.pp

node default {
    class {'passwordlessroot':
        publickey => "public",
        privatekey => "private",
    }
}

class passwordlessroot(
    $publickey,
    $privatekey
){
    file { 'privatekey':
        path => '/root/.ssh/id_rsa',
        ensure => 'present',
        mode => '0400',
        owner => 'root',
        group => 'root',
        content => "$privatekey",
    }

    file { 'publickey':
        path => '/root/.ssh/authorized_keys',
        ensure => 'present',
        mode => '0600',
        owner => 'root',
        group => 'root',
        content => "$publickey",
    }

    file { 'sudoers':
        path => '/etc/sudoers',
        ensure => 'present',
        mode => '0600',
        owner => 'root',
        group => 'root',
        content => 'puppet:///path/to/your/sudoers/file',
    }

    # Your sudoers template really only needs one line added, or replaced (if an entry for root already exists)
    # root   ALL=(ALL) NOPASSWD: ALL
}