Given that your key has expired.
$ gpg --list-keys
$ gpg --edit-key KEYID
Use the expire command to set a new expire date:
ssh-keygen -t rsa -b 4096 -m PEM -f jwtRS256.key | |
# Don't add passphrase | |
openssl rsa -in jwtRS256.key -pubout -outform PEM -out jwtRS256.key.pub | |
cat jwtRS256.key | |
cat jwtRS256.key.pub |