Unlike the _server auth TLS_ that's typical with web browsers, where the browser authenticates the server but not vice versa, _mutual TLS_ (mTLS) connections have both remote peers (client and server) authenticate to one another by presenting certificates. mTLS is not a different protocol. It's just a variant of TLS that's not usually turned on by default. This respository demonstrates **how to turn on mTLS** with different tools and languages. It also demonstrates other **TLS best practices** like certificate rotation.
mTLS provides _authenticated encryption_: an _identity dialtone_ and _end-to-end encryption_ for your workloads. It's like a secure line with caller ID. This has [all sorts of benefits](https://smallstep.com/blog/use-tls.html): better security, compliance, and easier auditability for starters. It **makes workloads identity-aware**, improving observability and enabling granular access control. Perhaps most compelling, mTLS lets you securely communicate with workloads running anywhere. Code, containers, devices, people, and anything else can connect securely using mTLS as long as they know one anothers' names and can resolve those names to routable IP addresses.
With properly configured mTLS, services can be safely exposed directly to the public internet: **only clients that have a certificate issued by the internal certificate authority will be allowed to connect**.
Here's a rough approximation of how an mTLS handshake works:
* It's the signing of random numbers that proves we're talking to the right remote. It's the digital equivalent of asking someone to send you a photo of them with today's newspaper.
* The client and server need to have prior knowledge of the root certificate(s) used for signing other certificates.
* The client and server need to be configured to use the correct certificate and private key (the certificate must have been issued by a CA with a trusted root certificate)
* Private keys are never shared. This is the magic of public key cryptography: unlike passwords or access tokens, certificates let you prove who you are without giving anyone the ability to impersonate you.
