Ensure old JWT tokens are seen as invalid

[christroutner]

The scope of this Issue is to create a test case to cover the use of old JWT tokens. It should test for the following use case:

• A user purchases their first JWT token.
• A user purchases a second JWT token.
• If the user uses the first JWT token, the system should recognize it as invalid, since it's been replaced by the second JWT token.

[christroutner]

Fixed by PR #5