I created an in-game bug reporter for Industries of Titan. Users can type in a message and it gets sent, along with a screenshot and a zip of their latest save to a server for us to look through.

This is an example of how to set up something similar in C++.

Update: @sswires89 pointed out that this relies on MimeHttpUpload.h which is currently only available through UDN. Sorry about the confusion!

BUIUploader.h

#pragma once

#include "Interfaces/IHttpRequest.h"
#include "HttpModule.h"
#include "UI/Util/MimeHttpUpload.h"
#include "BUIUploader.generated.h"

class UBUIUploader
{
	GENERATED_BODY()
public:
	UBUIUploader( const FObjectInitializer& ObjectInitializer );

	FOnMimeUploadHttpRequestComplete RequestCompleteDelegate;

	void SendReport();
}

BUIUploader.cpp

#include "BUIUploader.h"

#include "Interfaces/IHttpResponse.h"
#include "UI/Util/MimeHttpUpload.h"
#include "Windows/WindowsPlatformMisc.h"
#include <GenericPlatformFile.h>

UBUIUploader::UBUIUploader( const FObjectInitializer& ObjectInitializer )
	: Super( ObjectInitializer )
{
	// This will be called when the HTTP post is complete
	RequestCompleteDelegate.BindUObject( this, &UBUIUploader::OnRequestComplete );
}

void UBUIUploader::SendReport()
{
	TSharedRef<FMimeHttpUpload> MimeUpload = FMimeHttpUpload::Create();

	// Basic string values
	MimeUpload->AddFormField( "my_key", "Hello World" );
	MimeUpload->AddFormField( "another_key", "Great" );

	// Take a screenshot
	FString RequestedScreenshotPath = FPaths::ScreenShotDir() / "my_screenshot.png";
	FScreenshotRequest::RequestScreenshot( RequestedScreenshotPath, true, true );

	// Add a screenshot
	TArray<uint8> ScreenshotRawData;
	FFileHelper::LoadFileToArray( ScreenshotRawData, *FScreenshotRequest::GetFilename() );
	MimeUpload->AddAttachment( "screenshot_file", "upload_screenshot.png", "image/png", ScreenshotRawData );

	// Add a zip
	const FString ZipFilePath = "Fill/This/In/my.zip";
	TArray<uint8> SaveZipRawData;
	FFileHelper::LoadFileToArray( SaveZipRawData, *ZipFilePath );
	MimeUpload->AddAttachment( "zip_file", Filename, "application/zip", SaveZipRawData );

	// Send the request
	TSharedRef<IHttpRequest> HttpRequest = FHttpModule::Get().CreateRequest();
	const FString Url = "http://some.server.com";
	MimeUpload->SetupHttpRequest( HttpRequest, Url, RequestCompleteDelegate );
	HttpRequest->ProcessRequest();
}

void UBUIUploader::OnRequestComplete( FHttpRequestPtr Request, FHttpResponsePtr Response, bool bWasSuccessful )
{
	// Did it work or not?
	if ( bWasSuccessful && Response.IsValid() )
	{
		UE_LOG( LogTemp, Warning, TEXT( "%s" ), *Response->GetContentAsString() );

		if ( EHttpResponseCodes::IsOk( Response->GetResponseCode() ) )
		{
			// Yay we were successful!
		}
	}
}