How to create a Json Web Token (JWT) using OpenSSL shell commands?

I was able to recreate the JWT from https://jwt.io/

In your example, there was a hidden newline on the user secret. So in the below, I also add on that newline, purely to recreate the desired output.Also the email address in your payload was not consistent, so for below I have used jordan@example.com.

I took a slightly different approach to the hmac step. I converted the user secret to hex bytes and used that as the key (using the hexkey option for the HMAC).

# Construct the headerjwt_header=$(echo -n '{"alg":"HS256","typ":"JWT"}' | base64 | sed s/\+/-/g | sed 's/\//_/g' | sed -E s/=+$//)# ans: eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9# Construct the payloadpayload=$(echo -n '{"email":"jordan@example.com"}' | base64 | sed s/\+/-/g |sed 's/\//_/g' |  sed -E s/=+$//)# ans: eyJlbWFpbCI6ImpvcmRhbkBleGFtcGxlLmNvbSJ9# Store the raw user secret (with example of newline at end)secret=$'bigsecretisveryhardtoguessbysneakypeopleright\n'# Note, because the secret may have newline, need to reference using form $"" echo -n "$secret"# Convert secret to hex (not base64)hexsecret=$(echo -n "$secret" | xxd -p | paste -sd "")# ans: 62696773656372657469737665727968617264746f67756573736279736e65616b7970656f706c6572696768740a# For debug, also display secret in base64 (for input into https://jwt.io/)echo -n "$secret" | base64# ans: Ymlnc2VjcmV0aXN2ZXJ5aGFyZHRvZ3Vlc3NieXNuZWFreXBlb3BsZXJpZ2h0Cg==# Calculate hmac signature -- note option to pass in the key as hex byteshmac_signature=$(echo -n "${jwt_header}.${payload}" |  openssl dgst -sha256 -mac HMAC -macopt hexkey:$hexsecret -binary | base64  | sed s/\+/-/g | sed 's/\//_/g' | sed -E s/=+$//)# Create the full tokenjwt="${jwt_header}.${payload}.${hmac_signature}"# ans: eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJlbWFpbCI6ImpvcmRhbkBleGFtcGxlLmNvbSJ9.C3MVjfmnul8dLNIgiv6Dt3jSefD07Y0QtDrOZ5oYSXo