I attempted to build the changes on an older platform (CentOS 6.6) and came to realize that gnutls_certificate_set_x509_key_mem2(), the GnuTLS function needed if specifying a password, is not available in earlier versions of the GnuTLS library. So I added another preprocessor check, around that function call, to verify that the GnuTLS version is 3 or above. If a password was provided to MHD and the GnuTLS version is too old, then an error is returned. Attached are some simple code diffs, relative to the current SVN baseline, for your consideration.