fnando / url_signature Goto Github PK

class Signer
    SIGNING_ALGORITHM = 'sha1'
    SIGNATURE_PARAM_NAME = 'signature'
    SPLIT_SIGNATURE_PATTERN = /&?signature=/ # for both "signature=abc" and "max-width=100&signature=abc"

    class InvalidSignature < StandardError; end

    def initialize(secret)
      @secret = secret
    end

    # Sign a URL
    # Only the path and query is signed, making it easier to change domains.
    #
    # @param url [String] unsigned url
    # @return [String] signed url
    def sign_url(url)
      raise ArgumentError unless url.is_a?(String)

      parsed = Addressable::URI.parse(url)

      if (parsed.query_values || {}).keys.include?(SIGNATURE_PARAM_NAME)
        raise ArgumentError, 'Cannot sign an url with query param `signature`'
      end

      # sort query params, based on encoded keys
      query_str = (parsed.query || '').split('&').sort.join('&')

      # join together the signed string (path + query params), in raw format (i.e. url-encoded)
      evaluated_string = (query_str.length > 0) ? "#{parsed.path}?#{query_str}" : parsed.path
      signature = compute_signature(evaluated_string)

      # append signature, should be last
      new_query = parsed.query || ''
      new_query += '&' unless new_query.length == 0
      new_query += "#{SIGNATURE_PARAM_NAME}=#{signature}"

      parsed.query = new_query
      parsed.to_s # return the signed url
    end

    # Verify a signed url
    #
    # @return [String] url with query-param signature, e.g. ?signature=abc
    def verify_signed_url!(url)
      raise ArgumentError unless url.is_a?(String)

      parsed = Addressable::URI.parse(url)

      unless (parsed.query_values || {}).keys.include?(SIGNATURE_PARAM_NAME)
        raise InvalidSignature, 'Missing signature query param'
      end

      # needed since we are using String#split below
      unless (parsed.query_values || {}).keys.last == SIGNATURE_PARAM_NAME
        raise InvalidSignature, 'Expected signature query param to be last'
      end

      # extract the signature from query string, leaving the original query string
      sans_signature, signature = (parsed.query || '').split(SPLIT_SIGNATURE_PATTERN)

      # sort query string before validating signature
      query_str = sans_signature.split('&').sort.join('&')

      # build a string with path plus query, e.g. `/files/123?expire-at=2012-03-01&max-width=300`
      evaluated_string = (query_str.length > 0) ? "#{parsed.path}?#{query_str}" : parsed.path

      unless compute_signature(evaluated_string) == signature
        raise InvalidSignature, 'Invalid signature provided'
      end
    end

    private

    def secret
      @secret
    end

    def compute_signature(string)
      OpenSSL::HMAC.hexdigest(SIGNING_ALGORITHM, secret, string)
    end
  end