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/web_backend.h

@@ -4,6 +4,8 @@
 
 #pragma once
 
+#include <functional>
+#include <future>
 #include <string>
 #include "common/common_types.h"
 
@@ -20,4 +22,18 @@ namespace WebService {
 void PostJson(const std::string& url, const std::string& data, bool allow_anonymous,
               const std::string& username = {}, const std::string& token = {});
 
+/**
+ * Gets JSON from services.citra-emu.org.
+ * @param func A function that gets exectued when the json as a string is received
+ * @param url URL of the services.citra-emu.org endpoint to post data to.
+ * @param allow_anonymous If true, allow anonymous unauthenticated requests.
+ * @param username Citra username to use for authentication.
+ * @param token Citra token to use for authentication.
+ * @return future that holds the return value T of the func
+ */
+template <typename T>
+std::future<T> GetJson(std::function<T(const std::string&)> func, const std::string& url,
+                       bool allow_anonymous, const std::string& username = {},
+                       const std::string& token = {});
+
 } // namespace WebService