Remove conditional check for params[:signature].

If the params have been passed to us but the signature is omitted that looks
like a malicious login attempt.

lib/shopify_api.rb

@@ -122,7 +122,7 @@ module ShopifyAPI
     def initialize(url, token = nil, params = nil)
       self.url, self.token = url, token
 
-      if params && params[:signature]
+      if params
         unless self.class.validate_signature(params) && params[:timestamp].to_i > 24.hours.ago.utc.to_i
           raise "Invalid Signature: Possible malicious login" 
         end

test/shopify_api_test.rb

@@ -17,5 +17,17 @@ class ShopifyApiTest < Test::Unit::TestCase
       session = ShopifyAPI::Session.new("testshop.myshopify.com", "any-token")
       assert session.valid?
     end
+    
+    should "not raise error without params" do
+      assert_nothing_raised do
+        session = ShopifyAPI::Session.new("testshop.myshopify.com", "any-token")
+      end
+    end
+    
+    should "raise error if params passed but signature omitted" do
+      assert_raises(RuntimeError) do
+        session = ShopifyAPI::Session.new("testshop.myshopify.com", "any-token", {'foo' => 'bar'})
+      end
+    end
   end
 end