Is `SSL_CTX_set_dh_auto` specified to be a macro in the API?
Yes currenty it is specified as a macro: https://www.openssl.org/docs/man3.0/man3/SSL_CTX_set_dh_auto.html
Typically applications should use well know DH parameters that have built-in support in OpenSSL. The macros SSL_CTX_set_dh_auto() and SSL_set_dh_auto() configure OpenSSL to use the default built-in DH parameters for the SSL_CTX and SSL objects respectively.