Fix the documentation for the sign parameter (#5)

* Fix the documentation for the sign parameter

Even thought the documentation says that you should include the leading "/" in practice you need to exclude it

* add missing test

* inspect

Author: MathieuLegault1

README.md

@@ -70,17 +70,17 @@ Then a request path like:
 
 will fail because the `sign` parameter is not present.
 
-**The HMAC-SHA256 hash is created by taking the URL path (including the leading /), the request parameters (alphabetically-sorted and concatenated with & into a string). The hash is then base64url-encoded.**
+**The HMAC-SHA256 hash is created by taking the URL path (excluding the leading /), the request parameters (alphabetically-sorted and concatenated with & into a string). The hash is then base64url-encoded.**
 
 ```elixir
-Base.url_encode64(:crypto.mac(:hmac, :sha256, "1234", "/resize" <> "quality=60&url=https://s3.ca-central-1.amazonaws.com/my_image.jpg&width=300"))
-# => "O8Xo9xrP0fM67PIWMIRL2hjkD_c5HzzBtRLfpo43ENY="
+Base.url_encode64(:crypto.mac(:hmac, :sha256, "1234", "resize" <> "quality=60&url=https://s3.ca-central-1.amazonaws.com/my_image.jpg&width=300"))
+# => "ku5SCH56vrsqEr-_VRDOFJHqa6AXslh3fpAelPAPoeI="
 ```
 
 Now this request will succeed!
 
 ```sh
-/imageproxy/resize?url=https://s3.ca-central-1.amazonaws.com/my_image.jpg&width=300&quality=60&sign=O8Xo9xrP0fM67PIWMIRL2hjkD_c5HzzBtRLfpo43ENY=
+/imageproxy/resize?url=https://s3.ca-central-1.amazonaws.com/my_image.jpg&width=300&quality=60&sign=ku5SCH56vrsqEr-_VRDOFJHqa6AXslh3fpAelPAPoeI=
 ```
 
 ## License

test/plug_image_processing/plug_image_processing_test.exs

@@ -20,5 +20,19 @@ defmodule PlugImageProcessingTest do
       assert {"width", "10"} in query_params
       assert {"url", "http://bucket.com/test.jpg"} in query_params
     end
+
+    test "valid with signature", %{config: config} do
+      url_signature_key = "12345"
+      config = Keyword.put(config, :url_signature_key, url_signature_key)
+
+      url = PlugImageProcessing.generate_url("http://example.com", config, :resize, %{url: "http://bucket.com/test.jpg", width: 10})
+
+      assert url ===
+               "http://example.com/imageproxy/resize?url=http%3A%2F%2Fbucket.com%2Ftest.jpg&width=10&sign=#{generate_signature_from_url(url_signature_key, "resizeurl=http%3A%2F%2Fbucket.com%2Ftest.jpg&width=10")}"
+    end
+  end
+
+  defp generate_signature_from_url(url_signature_key, url) do
+    Base.url_encode64(:crypto.mac(:hmac, :sha256, url_signature_key, url))
   end
 end