May 25, 2024


I’m pleased to share that Azure Utility Gateway now helps mutual transport layer safety (mTLS) and on-line certificates standing protocol (OCSP). This was one of many key questions from our clients as they had been searching for safer communication choices for the cloud workloads. Right here, I cowl what mTLS is, the way it works, when to contemplate it, and how one can confirm it in Utility Gateway.

What’s mTLS?

Mutual transport layer safety (TLS) is a communication course of the place each events confirm and authenticate one another’s digital certificates previous to establishing an encrypted TLS connection. mTLS is an extension of the usual TLS protocol, and it gives an extra layer of safety over TLS. With conventional TLS, the server is authenticated, however the consumer isn’t. Because of this anybody can hook up with the server and provoke a safe connection, even when the consumer or person isn’t approved to take action. By utilizing mTLS you’ll be able to make it possible for each the consumer and the server should authenticate one another previous to establishing the safe connection, this can ensure there isn’t any unauthorized entry attainable on both aspect. mTLS works on the framework of zero belief—by no means belief, all the time confirm. This framework ensures that no connection needs to be trusted mechanically.

How does mTLS work?

mTLS works through the use of a mix of safe digital certificates and personal keys to authenticate each the consumer and the server. The consumer and the server every have their very own digital certificates and personal key, that are used to determine belief and a safe connection. The consumer verifies the server’s certificates, and the server verifies the consumer’s certificates—this ensures that each events are who they declare to be.

How are TLS and mTLS totally different?

TLS and mTLS protocols are used to encrypt community communication betweenclient and server. In TLS protocol solely the consumer verifies the validity of the server previous to establishing the encrypted communication. The server doesn’t validate the consumer throughout the TLS handshake. mTLS, on different hand, is a variation of TLS that provides an extra layer of safety by requiring mutual authentication between consumer and server. Because of this each the consumer and server should current a sound certificates earlier than the encrypted connection might be established. This makes mTLS safer than TLS because it provides an added layer of safety by validating authenticity of consumer and server.

TLS name stream:


Above flow diagram shows steps that are involved in establishing TLS connection between Client and Application GW

mTLS name stream:



Above flow diagram shows steps that are involved in establishing mutual TLS (mTLS)  connection between Client and Application GW

When to contemplate mTLS

  • mTLS is beneficial the place organizations comply with a zero-trust method. This manner a server should guarantee of the validity of the precise consumer or machine that wishes to make use of server info. For instance, a corporation could have an online utility that workers or shoppers can use to entry very delicate info, similar to monetary knowledge, medical information, or private info. By utilizing mTLS, the group can make sure that solely approved workers, shoppers, or gadgets are capable of entry the online utility and the delicate info it accommodates.
  • Web of Issues (IoT) gadgets discuss to one another with mTLS. Every IoT machine presents its personal certificates to one another to get authenticated.
  • Most new purposes are engaged on microservices-based structure. Microservices talk with one another by way of utility programming interfaces (APIs), through the use of mTLS you’ll be able to make it possible for API communication is safe. Additionally, through the use of mTLS you can also make positive malicious APIs aren’t speaking together with your APIs
  • To stop varied assaults, similar to brute power or credential stuffing. If an attacker can get a leaked password or a BOT tries to power its method in with random passwords, it will likely be of no use—and not using a legitimate TLS certificates the attacker will be unable to go the TLS handshake.

At excessive stage now you perceive what’s mTLS and the way it affords safer communication by following zero belief safety mannequin. In case you are new to Utility Gateway and have by no means setup TLS in Utility Gateway, comply with the hyperlink to create APPGW and Backend Servers. This tutorial makes use of self-signed certificates for demonstration functions. For a manufacturing atmosphere, use publicly trusted CA-signed certificates. As soon as end-to-end TLS is ready up, you’ll be able to comply with this hyperlink for establishing mTLS. To check this setup the prerequisite is to have OpenSSL and curl instrument put in in your machine. It is best to have entry to the consumer certificates and consumer personal key.

Let’s dive into how one can take a look at mTLS Utility Gateway. Within the command beneath, the consumer’s personal secret’s used to create a signature for the Certificates Confirm message. The personal key doesn’t go away the consumer machine throughout the mTLS handshake.

Confirm your mTLS setup through the use of curl/openssl

  • curl -vk https://<> –key consumer.key –cert consumer.crt

    <> -> Your area tackle

    consumer.key -> Shopper’s personal key

    consumer.crt -> Shopper certificates


Within the above output, we’re verifying if mTLS is appropriately arrange. Whether it is arrange appropriately, throughout the TSL handshake server will request the consumer certificates. Subsequent, within the handshake, you’ll want to confirm if the consumer has offered a consumer certificates together with the Certificates Confirm message. Because the consumer certificates was legitimate, the handshake was profitable, and the appliance has responded with an HTTP “200” response.

If the consumer certificates isn’t signed by the foundation CA file that was uploaded as per the hyperlink in step eight, the handshake will fail. Beneath is the response we’ll get if the consumer certificates isn’t legitimate.


Alternatively, you’ll be able to confirm the mTLS connectivity with an OpenSSL command.

  • openssl s_client -connect <IPaddress> :443 -key consumer.key -cert consumer.crt


As soon as the SSL connection is established sort as written beneath:

GET / HTTP/1.1

Host: <IP of host>


It is best to get the Response code—200. This validates that mutual authentication is profitable.


I hope you’ve gotten realized now what mTLS is, what downside it solves, how one can set it up in Utility Gateway and how one can validate the setup.  It is without doubt one of the a number of nice options of Utility gateway that gives our buyer with an additional layer of safety for the varied use circumstances that we now have mentioned above. One factor to notice is that at the moment Utility Gateway helps mTLS in frontend solely (between consumer and Utility gateway). In case your backend server is anticipating a consumer certificates throughout SSL negotiation between Utility gateway and backend server, that request will fail. If you wish to discover ways to ship certificates to backend utility by way of http header please watch for our subsequent weblog of  mTLS collection. In that weblog I’ll go over how one can use Rewrite function to ship the consumer certificates as http header. Additionally we’ll focus on how we are able to do OCSP validation of consumer certificates.


Study extra and get began with Azure Utility Gateway

What’s Azure Utility Gateway | Microsoft Study

Overview of mutual authentication on Azure Utility Gateway | Microsoft Study

Continuously requested questions on Azure Utility Gateway | Microsoft Study


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