Taken from: https://medium.com/@wintermeyer/goodbye-secrets-welcome-credentials-f4709d9f4698

Once you installed Rails 5.2 each of your new Rails projects has an already good to go setup for using credentials. No more generating keys manually. The important master key is automatically generated and stored in the file config/master.key which can be shared with other developers in the team but which should never be checked into the Git repository. The default .gitignore has been updated accordingly:

Ignore master key for decrypting credentials and more.

/config/master.key

Editing Credentials

All credentials are stored encrypted in the file config/credentials.yml.enc. Obviously you can not edit the file directly. You have to use the command rails credentials:editto edit them. For that to work you have to set the shell environment variable EDITOR first. Or you can do both with this one liner in your Bash shell:

$ EDITOR=nano rails credentials:edit

Now you can edit your credentials in yaml format. In this example I add a credential with the name foobar and the value test:

# aws:  
# access_key_id: 123  
# secret_access_key: 345# Used as the base secret for all MessageVerifiers in Rails, including the one protecting cookies.  
secret_key_base: 9846dad34a3168…68d634f  
foobar: test

Accessing Credentials

You can access a credential anywhere in your application with AppName::Application.credentials.name_of_the_credential. An example from within the console:

$ rails console  

Running via Spring preloader in process 19662  
Loading production environment (Rails 5.2.0)  
>> Shop::Application.credentials.foobar
=> “test”  
>> exit

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Server

To use the credentials in production you have to copy the config/master.keyfile to your production environment or setting it up with an environment variable.