March 29, 2019

Microsoft Azure Web App Service SSL/TLS Security using Cloudflare - C# ASP.Net MVC Core

SSL/TLS certificate & DDOS protection required? Simon Gilbert details Cloudflare on a Microsoft Azure Web App Service running C# ASP.Net MVC Core

Microsoft Azure Web App Service SSL/TLS Security using Cloudflare - C# ASP.Net MVC Core

Security Without Obscurity

Last year Google Chrome 68 was released with one of the main features being the browsers ability to call out websites that follow the HTTP protocol…and therefore lack a valid SSL/TLS certificate. Without this certificate, the site isn’t running HTTPS and your data isn’t encrypted end-to-end (including your bank details when you buy that new item from

SSL/TLS Certificate

Unfortunately there is much more to securing your platform that just running HTTPS, and we’re now in an age that security through obscurity will no longer suffice, particularly when it comes to man-in-the-middle and distributed denial of service (DDOS) attack protection.

When we launched my first startup Patrius a few years ago, we were in fact on the receiving end of intermittent DDOS attacks. We learnt a lot from it, not least how capable (and expensive) auto-scaling can be when you're running a load-balanced distributed system globally in the cloud.

DDOS Cyber Attack

When your servers are getting hammered the first necessity is to assess the traffic patterns to arrive at the point of threat detection. Following this is the examination point to understand and separate human traffic from the illegal stuff, and then filter it using deep packet inspection and rate limiting. Sounds complicated right? ...Indeed, and we were two devs in a London flat simply trying to introduce ad-fraud detection algorithms and low latency into the AdTech industry. We needed a third party to help mitigate the cyber attacks...

Enter “Cloudflare”…

“Cloudflare protects and accelerates any website online. Its web traffic is routed through our intelligent global network, allowing us to block threats and limit abusive bots and crawlers from wasting your bandwidth and server resources.”

...With Cloudflare it isn't just about security, it's about performance too. However, the functioning of the internet is dependent on DNS, and unfortunately given that DNS was designed in the 1980's when security was not a primary concern, it isn't secure by design, making it easy for an attacker to masquerade as an authoratative server. Fortunately, Cloudflare provide DNSSEC protection -

"If DNS is the phone book of the Internet, DNSSEC is the Internet’s unspoofable caller ID. It guarantees a web application’s traffic is safely routed to the correct servers so that a site’s visitors are not intercepted by a hidden “man-in-the-middle” attacker."


The Domain Name System Security Extensions (DNSSEC) strengthens authentication in DNS by using digital signatures based on public key cryptography.

"With DNSSEC, it's not DNS queries and responses themselves that are cryptographically signed, but rather DNS data itself is signed by the owner of the data."

Cloudflare sounds amazing doesn't it? I agree…so let’s look at enabling Cloudflare on a Microsoft Azure Web App Service deployment running C# ASP.Net MVC Core...

I'm going to assume that you're already running an existing Microsoft Azure Web App.

Let's Get Secure...

First step, DNS hostname mapping for your Web App in Azure (Cloudflare won't accept the default URL).

Azure App Service Hostname

Let's check that it's mapped correctly...

Azure App Service - Deployed

The next step is to deploy your ASP.Net MVC Core source code and then head over to Cloudflare and create a free account. We can then add our site and start the process of securing our platform.

Cloudflare Platform

Now we will observe Cloudflare's process of running a DNS query against your domain to assess exactly what their system has to work with.

Cloudflare DNS Query Results

...You will then be asked to switch your name servers to using Cloudflare's instead (the names they've used are amusing!)

Cloudflare Name Servers

Once this step is validated, you'll be informed that Cloudflare is now protecting your site.

Cloudflare Protection Active

At this point it's time to fully activate the free TLS certificate from Cloudflare by clicking on the security link and going to the "Crypto" section.

Cloudflare SSL/TLS Certificate - Pending

Your TLS certificate will be activated a short time after this, and at this point you're running HTTPS end-to-end.

Cloudflare SSL/TLS Certificate - Active

A quick check of the TLS certificate in the browser on our production domain -

Cloudflare SSL/TLS Certificate - In Browser

...Awesome, our HTTPS config is live!!!

Configuring Our Security Further

Let's ensure that HTTP isn't an option anymore, and enforce redirects on all HTTP requests to go through the HTTPS scheme instead.

Cloudflare Protection - HTTPS

Now to enforce strict transport security (HSTS) also...

Cloudflare Protection - HSTS

Click enable, and we'll configure the settings. The header max age setting at this stage should be fine as 6 months. The other point to note is the subdomain setting - Let's enforce that too.

Cloudflare Protection - HSTS Configuration

Next is the TLS version, which is currently in production as version 1.3 since 2018. Given that TLS 1.2 was released in 2008 you'd really expect most users to be running TLS 1.3 as a minimum at this stage.

Cloudflare Protection - TLS Version

HTTPS rewrites are next. There's no point running TLS if you're going to be hitting JavaScript and CSS resources over HTTP...and this also ties into cross-site scripting (XSS).

Cloudflare Protection - HTTPS Rewrites

Our Cloudflare Statistics

Now that's configured, let's review some stats on Cloudflare's dashboard for our production domain. As you can see, we're already being hit by traffic from different countries.

Cloudflare Protection - Web Traffic Requests

Interestingly we can already see the performance side of Cloudflare kicking in with it's CDN and caching functionality.

Cloudflare Protection - Cache Performance Stats

...So far, we've achieved a free TLS Certificate and some performance improvements. Let's see if Cloudflare has needed to mitigate anything yet...

Cloudflare Protection - Threats Mitigated

...and that's exactly the point - You cannot assume security in the the modern digital world...kinda terrifying.

Mitigating A DDoS Attack Using Cloudflare

Before we wrap things up, the most important part in all of this is the ability to pull the trigger on a DDoS attack. You've already loaded the Cloudflare gun, so in the event that you do need to help mitigate an attack with immediate this button.

Cloudflare Protection - Under Attack Mode On

This will lead to you being in DDoS Attack mode, which will force all visitors to your site to be shown a JavaScript challenge...

Cloudflare Protection - Under Attack Mode

Today we've covered the basics using a free account. Upgrading to a business account offers many more security protection and performance features for your platform. Enjoy!