You are using staging server - a separate instance of the ESP Component Registry that allows you to try distribution tools and processes without affecting the real registry.
# mbedtls_cxx This is a simplified C++ wrapper of mbedTLS for performing TLS and DTLS handshake a communication. This component allows for overriding low level IO functions (`send()` and `recv()`) and thus supporting TLS over various physical channels.
idf.py add-dependency "espressif/mbedtls_cxx^0.1.0"