Add support for HMAC-SHA256 (#15)

lib/oauther.ex

@@ -13,7 +13,7 @@ defmodule OAuther do
             consumer_secret: String.t(),
             token: nil | String.t(),
             token_secret: nil | String.t(),
-            method: :hmac_sha1 | :rsa_sha1 | :plaintext
+            method: :hmac_sha1 | :hmac_sha256 | :rsa_sha1 | :plaintext
           }
   end
 
@@ -62,7 +62,14 @@ defmodule OAuther do
   def signature(verb, url, params, %Credentials{method: :hmac_sha1} = creds) do
     creds
     |> compose_key()
-    |> hmac_sha(base_string(verb, url, params))
+    |> hmac_sha(base_string(verb, url, params), :sha)
+    |> Base.encode64()
+  end
+
+  def signature(verb, url, params, %Credentials{method: :hmac_sha256} = creds) do
+    creds
+    |> compose_key()
+    |> hmac_sha(base_string(verb, url, params), :sha256)
     |> Base.encode64()
   end
 
@@ -74,12 +81,12 @@ defmodule OAuther do
 
   # TODO: Remove this once we require at minimum OTP 22.
   if Code.ensure_loaded?(:crypto) and function_exported?(:crypto, :mac, 4) do
-    defp hmac_sha(key, data) do
-      :crypto.mac(:hmac, :sha, key, data)
+    defp hmac_sha(key, data, hash_function) do
+      :crypto.mac(:hmac, hash_function, key, data)
     end
   else
-    defp hmac_sha(key, data) do
-      :crypto.hmac(:sha, key, data)
+    defp hmac_sha(key, data, hash_function) do
+      :crypto.hmac(hash_function, key, data)
     end
   end
 
@@ -179,6 +186,7 @@ defmodule OAuther do
 
   defp signature_method(:plaintext), do: "PLAINTEXT"
   defp signature_method(:hmac_sha1), do: "HMAC-SHA1"
+  defp signature_method(:hmac_sha256), do: "HMAC-SHA256"
   defp signature_method(:rsa_sha1), do: "RSA-SHA1"
 
   defp percent_encode({key, value}) do

test/oauther_test.exs

@@ -14,6 +14,20 @@ defmodule OAutherTest do
     assert signature(params, creds, "/photos") == "tR3+Ty81lMeYAr/Fid0kMTYa/WM="
   end
 
+  test "HMAC-SHA256 signature" do
+    creds =
+      OAuther.credentials(
+        method: :hmac_sha256,
+        consumer_secret: "kd94hf93k423kf44",
+        token_secret: "pfkkdhi9sl3r4s00",
+        consumer_key: "dpf43f3p2l4k3l03",
+        token: "nnch734d00sl2jdk"
+      )
+
+    params = protocol_params(creds)
+    assert signature(params, creds, "/photos") == "WVPzl1j6ZsnkIjWr7e3OZ3jkenL57KwaLFhYsroX1hg="
+  end
+
   test "RSA-SHA1 signature" do
     creds =
       OAuther.credentials(