=== Storing Encrypted Credentials in Source Control

The Rails `credentials` commands provide access to encrypted credentials,
so you can safely store access tokens, database passwords, and the like
safely inside the app without relying on a mess of ENVs.

This also allows for atomic deploys: no need to coordinate key changes
to get everything working as the keys are shipped with the code.

=== Setup

Applications after Rails 5.2 automatically have a basic credentials file generated
that just contains the secret_key_base used by MessageVerifiers/MessageEncryptors, like the ones
signing and encrypting cookies.

For applications created prior to Rails 5.2, we'll automatically generate a new
credentials file in `config/credentials.yml.enc` the first time you run `bin/rails credentials:edit`.
If you didn't have a master key saved in `config/master.key`, that'll be created too.

Don't lose this master key! Put it in a password manager your team can access.
Should you lose it no one, including you, will be able to access any encrypted
credentials.

Don't commit the key! Add `config/master.key` to your source control's
ignore file. If you use Git, Rails handles this for you.

Rails also looks for the master key in `ENV["RAILS_MASTER_KEY"]`, if that's easier to manage.

You could prepend that to your server's start command like this:

   RAILS_MASTER_KEY="very-secret-and-secure" server.start

=== Set up Git to Diff Credentials

Rails provides `rails credentials:diff --enroll` to instruct Git to call `rails credentials:diff`
when `git diff` is run on a credentials file.

Running the command enrolls the project such that all credentials files use the
"rails_credentials" diff driver in .gitattributes.

Additionally since Git requires the driver itself to be set up in a config file
that isn't tracked Rails automatically ensures it's configured when running
`credentials:edit`.

Otherwise each co-worker would have to run enable manually, including on each new
repo clone.

=== Editing Credentials

This will open a temporary file in `$EDITOR` with the decrypted contents to edit
the encrypted credentials.

When the temporary file is next saved the contents are encrypted and written to
`config/credentials.yml.enc` while the file itself is destroyed to prevent credentials
from leaking.

=== Environment Specific Credentials

The `credentials` command supports passing an `--environment` option to create an
environment specific override. That override will take precedence over the
global `config/credentials.yml.enc` file when running in that environment. So:

   bin/rails credentials:edit --environment development

will create `config/credentials/development.yml.enc` with the corresponding
encryption key in `config/credentials/development.key` if the credentials file
doesn't exist.

The encryption key can also be put in `ENV["RAILS_MASTER_KEY"]`, which takes
precedence over the file encryption key.

In addition to that, the default credentials lookup paths can be overridden through
`config.credentials.content_path` and `config.credentials.key_path`.
