A recent contribution by Chan Shih-Ping added a new module, respectively tls_wolfssl:
It offers an alternative to the tls module using the library from wolfssl project, the tls module is using the libssl.
Expect changes in the module, being still work in progress, but it is already in a usable state and help with testing would be very appreciated.
At this stage, you can provide feedback on this module on the issue tracker opened for this purpose:
Or email your remarks to sr-dev@lists.kamailio.org list.
Thanks for flying Kamailio!