PDF invoices doesn't have auth mechanism

Issue

If the pdf invoice URL is known or guessed, the invoice can be seen without any authentication.

A Red Hat subscription provides unlimited access to our knowledgebase, tools, and much more.

Here are the common uses of Markdown.

Code blocks

~~~
Code surrounded in tildes is easier to read
~~~

Links/URLs

[Red Hat Customer Portal](https://access.redhat.com)