char cookiehash[64];
memcpy(buf, cookie, 18);
memcpy(buf + 18, fingerprint, sizeof(buf) - 18);
sha512(buf, sizeof(buf), cookiehash);
b64encode_urlsafe(cookiehash, cookiehash, 18);
char cookiehash[64];
memcpy(buf, cookie, 18);
memcpy(buf + 18, fingerprint, sizeof(buf) - 18);
sha512(buf, sizeof(buf), cookiehash);
b64encode_urlsafe(cookiehash, cookiehash, 18);