jwt_token_creation.txt

HS256 - Signature:

echo -n "<JWT Base64url encoded - Header.Payload>" | openssl dgst -sha256 -hmac '<SECRET>' -binary | openssl base64 

The output of the signature will give base64 encoding, convert that to base64url encoding

SZf1eovdqV+1mo8rvI79UxQT3Ue/mJd3ipXu8XO01os=

Change (+ to -), (/ to _), (Omit the padding == or =)

SZf1eovdqV-1mo8rvI79UxQT3Ue_mJd3ipXu8XO01os

Automating the base64url encoding:

echo -n "<JWT Header.Payload" | openssl dgst -sha256 -hmac '<SECRET>' -binary | openssl base64 -e -A | sed 's/\+/-/g' | sed 's/\//_/g' | sed -E 's/=+$//' | xargs

RS256 - Signature:

Priv and Pub Key Generations

openssl genrsa -out private.pem 2048
openssl rsa -in private.pem -out public.pem -pubout -outform PEM

Signing with the Priv key
echo -n "<JWT Base64url encoded - Header.Payload>" | openssl dgst -sha256 -sign private.pem | openssl base64 -e -A | sed 's/\+/-/g' | sed 's/\//_/g' | sed -E 's/=+$//' | xargs