Transport Layer Security (TLS), the successor of Secure Socket Layer (SSL), is the mechanism through which encrypted connections can be established between clients and servers on the web and through which data can flow with integrity intact.
Simplified, TLS is made possible by using a Public Key Infrastructure (PKI) involving private cryptographic keys, certificates of ownership (public, signed with private key), and certificate authorities (CAs, issuing and asserting the validity of issued certificates).
The entire system depends on the functioning operation of the CAs. The system trusts that the cryptographic keys that CAs use to sign certificates of ownership to site/domain owners are kept secret. It also depends on the domain owners' ability to keep their private cryptographic keys secret.
If they fail to do so, they have to report the leak to the CA that issued the certificate. After this disclosure, the CA can revoke the certificate and, in doing so, let browsers and other clients know of the changes through the Online Certificate Status Protocol (OCSP).
By default and without any special configuration, k6 connects and talks to servers over TLS. You just need to make sure that you specify your request URLs with the https scheme.
K6 supports the following TLS functionalities. Each is worth discussing in more detail: