Example of how to dynamically set a rails secret_token per-heroku app instance. This sets a heroku environment variable on deployment, which is attempted to be read as a secret_token key file. If the token is not found, a new one is generated on the fly (draw back here is that a dynamic secret_key is used every time the app restarts, causing all…

push_to_heroku.rake

desc 'Pushes to heroku demo app'
task :push_to_demo => :environment do |t, args|
	app_name = 'demo'
	push app_name
end

def push(app_name)
	puts "$$$$$$$$$$ Pushing to heroku app: #{app_name}"

	puts "$$$$$ Pushing to heroku app: #{app_name}"
	Bundler.clean_exec "git push git@heroku.com:#{app_name}.git && " << \
			   "heroku config:add MY_APP_NAME='#{app_name}' --app #{app_name}"
end

secret_token.rb

# initializers/secret_token.rb
class ConfigurationError < StandardError; end

require 'securerandom'
require 'yaml'

secret_token_file = 'config/secret_token.yml'
app_name_key = "MY_APP_NAME"
app_name = "my_app"

if ENV[app_name_key]
	app_name = ENV[app_name_key]	
end

secret_token = YAML::load(File.open(secret_token_file))[app_name] if File.exists?(secret_token_file) || SecureRandom.hex(64)
raise ConfigurationError.new("Could not load or set secret token from environment or #{File.expand_path(secret_token_file)}") unless secret_token
 
MyApp::Application.config.secret_token = secret_token

secret_token.yml

# config/secret_token.yml

# run ">rake secret" to generate a new secret key, as needed.

# default_key
my_app: c6999d5d0a4dd4465fc90b21baa881bf91ba56c5490040300a1847819fc0036abd8a865abc4a2aa5a3f36dbcfd9f53029b38bfa1706ff4919557d07f413dd982

demo: 130e4c313d6d3b427b5ef94849dbebfb4be50c1fd66ecb4dbe6583dc345f558a9d2f46855e0feff0b9510477bf2e6758d5220daf39707d74c586063d4fd59477

Some credit to @elvanja for his blog post here.