startup: load configuration (public key) at startup time (#10)

This commit moves the parsing of the public key configuration during
the loading of the proxy file (instead of during runtime while a
request is made to the proxy).

proxy_server.rb

@@ -15,7 +15,9 @@ class ProxyServer < Sinatra::Base
   # set :logging, true
 
   # Secret key for JWT verification
-  PUBLIC_KEY = ENV.fetch("JWT_SIGNING_PUBLIC_KEY").gsub("\\n", "\n")
+  PUBLIC_KEY = OpenSSL::PKey.read(
+    ENV.fetch("JWT_SIGNING_PUBLIC_KEY").gsub("\\n", "\n")
+  ).freeze
 
   error JWT::ExpiredSignature do
     halt 401, {error: "Token has expired"}.to_json
@@ -49,11 +51,10 @@ class ProxyServer < Sinatra::Base
 
       # Verify JWT token
       begin
-        public_key = OpenSSL::PKey.read(PUBLIC_KEY)
         # JWT.decode returns [payload, headers]
         @payload, _ = JWT.decode(
           token,
-          public_key,
+          ::ProxyServer::PUBLIC_KEY,
           true, # Verify signature
           {
             required_claims: ["exp", "verb", "path", "servers"],

spec/proxy_server_spec.rb

@@ -384,4 +384,43 @@ def expect_json_body(k, v)
       end
     end
   end
+
+  context "startup of ProxyServer" do
+    def load_config(writer, config)
+      fork do
+        begin
+          stub_const('ENV', config)
+          load File.expand_path("./proxy_server.rb"), true
+          writer.write "success!\n"
+        rescue
+          writer.write "fail: #{$!.message}\n"
+        end
+        writer.close
+      end
+    end
+
+    context "with an incorrect configuration" do
+      it "should raise an error" do
+        # IO.pipe is used to share data between the forked processes
+        rd, writer = IO.pipe
+        load_config(writer, { 'JWT_SIGNING_PUBLIC_KEY' => 'OUPS-INCORRECT' })
+        writer.close
+
+        expect(rd.read).to eq("fail: Could not parse PKey\n")
+      end
+    end
+
+    context "with an correct configuration" do
+      it "should load without any error" do
+        # IO.pipe is used to share data between the forked processes
+        rd, writer = IO.pipe
+        rsa_key = OpenSSL::PKey::RSA.new(2048)
+        load_config(writer, { 'JWT_SIGNING_PUBLIC_KEY' => rsa_key.public_key.to_pem })
+        writer.close
+
+        expect(rd.read).to eq("success!\n")
+      end
+    end
+  end
+
 end