WebService: Verify username and token (#2930)

* WebService: Verify username and token; Log errors in PostJson

* Fixup: added docstrings to the functions

* Webservice: Added Icons to the verification, imrpved error detection in cpr, fixup nits

* fixup: fmt warning

src/web_service/verify_login.h

@@ -0,0 +1,24 @@
+// Copyright 2017 Citra Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <functional>
+#include <future>
+#include <string>
+
+namespace WebService {
+
+/**
+ * Checks if username and token is valid
+ * @param username Citra username to use for authentication.
+ * @param token Citra token to use for authentication.
+ * @param endpoint_url URL of the services.citra-emu.org endpoint.
+ * @param func A function that gets exectued when the verification is finished
+ * @returns Future with bool indicating whether the verification succeeded
+ */
+std::future<bool> VerifyLogin(std::string& username, std::string& token,
+                              const std::string& endpoint_url, std::function<void()> func);
+
+} // namespace WebService