KDF_F_PKEY_TLS1_PRF_DERIVE

Undocumented in source but is binding to C. You might be able to learn more by searching the web for its name.
extern (C) nothrow
static if(!(OPENSSL_VERSION_AT_LEAST(1, 1, 1)))
enum KDF_F_PKEY_TLS1_PRF_DERIVE = 101;

Meta