To generate a signature, ensure that your version of chat-attestation is up to date and then locate your chat-attestation.priv.key and run the following command:

echo -n '59890938cd73beb0d190bcfa06e2bfa6' > /tmp/challenge.txt && openssl pkeyutl -sign -inkey YOUR_PATH_HERE -out - -rawin -in /tmp/challenge.txt | base64 -w 0 - && rm /tmp/challenge.txt

and copy the output of that command into the signature box.