feat: add sha256 signatures to outgoing http requests (#2874)

spec/lib/postal_spec.rb

@@ -0,0 +1,12 @@
+# frozen_string_literal: true
+
+require "rails_helper"
+
+RSpec.describe Postal do
+  describe "#signer" do
+    it "returns a signer with the installation's signing key" do
+      expect(Postal.signer).to be_a(Signer)
+      expect(Postal.signer.private_key.to_pem).to eq OpenSSL::PKey::RSA.new(File.read(Postal::Config.postal.signing_key_path)).to_pem
+    end
+  end
+end