Upgrade credential system to work with Rails 5.2

[peterkos]

https://medium.com/cedarcode/rails-5-2-credentials-9b3324851336

[cbaudouinjr]

Blocked by #291 as additional documentation will be needed for the user during setup.

[cbaudouinjr]

Not too sure what the best implementation is for this as we are a unique Rails application. There are a limited number of ways we can implement this that don't add any extra burden on the end user.

• Create a credentials.rb.enc file ourselves where secret_key_base and devise_secret_key simply point to the pre-existing environment variables for SECRET_KEY_BASE and DEVISE_SECRET_KEY and distribute the master key in our docs. This is probably the easiest as the only environment variable they would have to add is MASTER_KEY, however, it is not good practice to distribute this master key.
• Have the user perform a deploy, enter a bash shell on the VM and generate the credentials files from scratch and perform a redeploy.

We can't ask the users to generate the credential files on their local machine (then push to their VM) as that would require them to install Ruby, Rails, etc.

Regardless we should find a solution for this before we migrate to Rails 6 #309.

[peterkos]

We can't ask the users to generate the credential files on their local machine (then push to their VM) as that would require them to install Ruby, Rails, etc.