oauth_signature.rb

require 'cgi'
require 'base64'
require 'openssl'

def oauth_url(url)
  parameters = ["oauth_consumer_key=#{ENV.fetch 'OAUTH_KEY'}",
                "oauth_nonce=#{Random.rand(100000000).to_s}",
                "oauth_signature_method=#{'HMAC-SHA1'}",
                "oauth_timestamp=#{Time.now.to_i.to_s}",
                "oauth_version=1.0"].join('&')

  base_string = ['GET', CGI.escape(url), CGI.escape(parameters)].join '&'

  ## Cryptographic hash function used to generate oauth_signature
  # by passing the secret key and base string. Note that & has
  # been appended to the secret key. Don't forget this!
  secret_key = "#{ENV.fetch('OAUTH_SECRET')}&"
  oauth_signature = CGI.escape(Base64.encode64(OpenSSL::HMAC.digest('sha1', secret_key, base_string)).chomp)

  "#{url}?#{parameters}&oauth_signature=#{oauth_signature}"
end