Create OAuth1.0 authentication header string

o_auth1.rb

class OAuth1
  class << self
    def oauth_header(uri:, method:, access_token:, access_secret:, consumer_key:, consumer_secret:)
      header = {
        'oauth_consumer_key'     => consumer_key,
        'oauth_token'            => access_token,
        'oauth_nonce'            => generate_nonce, 
        'oauth_signature_method' => 'HMAC-SHA256',
        'oauth_timestamp'        => Time.now.to_i,
        'oauth_version'          => '1.0'
      }

      signature_base = signature_base_string(method.to_s.upcase, uri, header)
      signing_key    = signature_key_string(consumer_secret, access_secret)

      header['oauth_signature'] = sign(signing_key, signature_base)

      stringified_header(header)
    end

    private

    def generate_nonce
      ERB::Util.url_encode(SecureRandom.base64)
    end

    def signature_base_string(method, uri, params)
      encoded_params = params.sort_by { |k, _| k }.map{ |k, v| "#{k}=#{v.to_s}" }.join("\&")
      "#{method}\&#{ERB::Util.url_encode(uri)}\&#{ERB::Util.url_encode(encoded_params)}"
    end

    def signature_key_string(consumer_secret, access_secret)
      "#{consumer_secret}\&#{access_secret}"
    end

    def sign(key, base_string)
      ERB::Util.url_encode(Base64.strict_encode64(OpenSSL::HMAC.digest('sha256', key, base_string)))
    end

    def stringified_header(header)
      stringified_header = header.sort_by { |k, _| k }.map{ |k, v| "#{k}=\"#{v.to_s}\"" }.join(",")
      "OAuth #{stringified_header}"
    end
  end
end