in unreal/OfflineMainMenuWidget.cpp [24:41]
void UOfflineMainMenuWidget::LoginRequest(FString usr, FString pwd) {
TSharedPtr<FJsonObject> JsonObject = MakeShareable(new FJsonObject());
JsonObject->SetStringField(TEXT("username"), *FString::Printf(TEXT("%s"), *usr));
JsonObject->SetStringField(TEXT("password"), *FString::Printf(TEXT("%s"), *pwd));
FString JsonBody;
TSharedRef<TJsonWriter<TCHAR>> JsonWriter = TJsonWriterFactory<>::Create(&JsonBody);
FJsonSerializer::Serialize(JsonObject.ToSharedRef(), JsonWriter);
TSharedRef<IHttpRequest, ESPMode::ThreadSafe> LoginHttpRequest = Http->CreateRequest();
LoginHttpRequest->SetVerb("POST");
LoginHttpRequest->SetURL(ApiGatewayEndpoint + LoginURI);
LoginHttpRequest->SetHeader("Content-Type", "application/json");
LoginHttpRequest->SetContentAsString(JsonBody);
LoginHttpRequest->OnProcessRequestComplete().BindUObject(this, &UOfflineMainMenuWidget::OnLoginResponse);
LoginHttpRequest->ProcessRequest();
}