Use a credential file on Heroku

README.md

How to use a credential file on Heroku (json, yml, etc.)

1. Add an initializer file to write the credentials file

# config/initializers/json_credentials.rb
filepath = './credentials.json'
File.write(filepath, ENV['YOUR_JSON_CREDENTIALS']) unless File.exists?(filepath)

2. Set the environment variable on Heroku

heroku config:set SOME_JSON_CREDENTIALS='{"key":"value"}'

Should work with multiline strings too:

heroku config:set YAML_CREDENTIALS='key1:
  key2: value
  a_list:
    - first_element
    - "second element"
    - boolean: true'

3. (Optional) Store the content of the file in your .env (not needed if you already have the credentials file locally)

YOUR_JSON_CREDENTIALS='{"key":"value"}' # content of the json file inside of single quotes

Don't forget to add the credentials file to your .gitignore!

Bonus: Escape special characters

In case you need to escape special characters (to store a YAML file in your .env for example), an easy way to get the escaped version of a file is to copy-paste the content as a string in irb:

# irb
[1] pry(main)> 'key1:
  key2: value
  a_list:
    - first_element
    - "second element"
    - boolean: true'
=> "key1:\n  key2: value\n  a_list:\n    - first_element\n    - \"second element\"\n    - boolean: true"

Use the resulting string when setting the environment variable in your .env:

# wrap the string in single quotes
YAML_CREDENTIALS='key1:\n  key2: value\n  a_list:\n    - first_element\n    - \"second element\"\n    - boolean: true'