SSL_get_shared_group
ngroups = SSL_get_shared_group(s, -1);
nid = SSL_get_shared_group(s, i);
#define SSL_get_shared_curve SSL_get_shared_group
SSL_group_to_name(serverssl, SSL_get_shared_group(serverssl, 0))))
shared_group0 = SSL_get_shared_group(serverssl, 0);