The documentation for CONFIG_MBEDTLS_PEM_CERTIFICATE_FORMAT in nRF Connect SDK says:
By default only DER (binary) format of certificates is supported. Enable this option to enable support for PEM format.
And lists, amongst other things, CONFIG_MBEDTLS_BUILTIN as a dependency. But in ncs, it seems the builtin MBEDTLS cannot be used, and CONFIG_MBEDTLS_LIBRARY_NRF_SECURITY is the default instead??
So after an hour of going around in circles with PEM, it seems it's simply not possible with MBEDTLS and the nRF Connect SDK. But I can't find a whisper on this topic anywhere, except a couple of words coming to a similar conclusion the PEM config here, and a comment on the BUILTIN clash and a strange diversion to OpenThread here. Surely I'm not the first to try to use PEM certificates for TLS with ncs?
At this stage I don't know which of these configs are leading me astray, or indeed whether it's specific to the nrf5340 I'm targeting (if so, why?).
