public unsafe static void SSL_CTX_set_alpn_select_cb(IntPtr ctx, alpn_select_cb_t cb, IntPtr arg)
 {
     NativeMethods.SSL_CTX_set_alpn_select_cb(ctx, cb, arg);
 }
 public static extern void SSL_CTX_set_alpn_select_cb(IntPtr ctx, alpn_select_cb_t cb, IntPtr arg);