OpenSLL eNULL ciphers

Hallo dear mailing list, This is my first ever message. So if I do something wrong, please be nice. I have the task to subscribe to a mosquito MQTT Server via TLS using a certificate authentication over SSL but without encryption. So I would want to use the NULL-SHA256 cipher. That is available on my system/the container. ( checked via openssl ciphers NULL) but if I call openssl_get_cipher_methods() it is not available. I used an alpine linux build, as they enable the --with-system-ciphers option to build php, but no effect. I think the Problem is that the default openssl ciphers don’t contain the eNULL or aNULL ciphers, as they are obviously not secure. And PHP is calling without parameters? There is no option to specify that I want eNULL in PHP, I think. Can somebody help me? Is my problem clearly stated? Best regards Frieder