Revert "Add token decoding functionality to login/registration views #153" and refactor into a better method

[ghost]

Before the Hawthorn release we did the following PR:

• Add token decoding functionality to login/registration views #153

I had a couple of notes that I want us to address:

• This PR has a couple of inline changes that would make it difficult to manage in future releases.
• Adding tests would make future merges easier to verify. This is a good mitigation even if it doesn't make them go away.
• I still need more background about the nature of the issue we're solving, but my initial though is that we could use "encoding" like Base64 instead of a shared-key "encryption".