I'm trying to create a JSON Web Token (JWT) using command line utilities on MacOS and hitting a snag with the signing portion.
I was greatly inspired by this gist: https://gist.github.com/indrayam/dd47bf6eef849a57c07016c0036f5207
For my JWT I have Header:
{"alg":"HS256","typ":"JWT"}
Payload:
{"email":"[email protected]"}
And my hmac secret is:
bigsecretisveryhardtoguessbysneakypeopleright
Or in base64:
Ymlnc2VjcmV0aXN2ZXJ5aGFyZHRvZ3Vlc3NieXNuZWFreXBlb3BsZXJpZ2h0Cg==
I was using the following site to validate: https://jwt.io/
I find that if I enter all of that into the site using the base64 version of my secret, it generates the following JWT that successfully verifies against the site I'm testing:
eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJlbWFpbCI6ImpvcmRhbkBleGFtcGxlLmNvbSJ9.C3MVjfmnul8dLNIgiv6Dt3jSefD07Y0QtDrOZ5oYSXo
In bash I tried this with:
jwt_header=$(echo -n '{"alg":"HS256","typ":"JWT"}' | base64 | sed s/\+/-/g | sed 's/\//_/g' | sed -E s/=+$//)
payload=$(echo -n '{"email":"[email protected]"}' | base64 | sed s/\+/-/g |sed 's/\//_/g' | sed -E s/=+$//)
hmac_signature=$(echo -n "${jwt_header}.${payload}" | openssl dgst -sha256 -hmac "${key}" -binary | openssl base64 -e -A | sed s/\+/-/g | sed 's/\//_/g' | sed -E s/=+$//)
jwt="${jwt_header}.${payload}.${hmac_signature}"
which produced the following:
eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJlbWFpbCI6ImpyZWVkQGV4dG9sZS5jb20ifQ.o426f0XDnsUwActVt14Cr3X3IUqPwfv6yaN5nRaZhew
Which is not accepted as valid by the site I'm posting to. So I'm unsure what I am doing wrong in the openssl command that is not getting a valid HS256 signature.
JSON web token (JWT), pronounced "jot", is an open standard (RFC 7519) that defines a compact and self-contained way for securely transmitting information between parties as a JSON object. Again, JWT is a standard, meaning that all JWTs are tokens, but not all tokens are JWTs.
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 [email protected]
.
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 header
jwt_header=$(echo -n '{"alg":"HS256","typ":"JWT"}' | base64 | sed s/\+/-/g | sed 's/\//_/g' | sed -E s/=+$//)
# ans: eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9
# Construct the payload
payload=$(echo -n '{"email":"[email protected]"}' | base64 | sed s/\+/-/g |sed 's/\//_/g' | sed -E s/=+$//)
# 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 "$secret" | base64
# ans: Ymlnc2VjcmV0aXN2ZXJ5aGFyZHRvZ3Vlc3NieXNuZWFreXBlb3BsZXJpZ2h0Cg==
# Calculate hmac signature -- note option to pass in the key as hex bytes
hmac_signature=$(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 token
jwt="${jwt_header}.${payload}.${hmac_signature}"
# ans: eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJlbWFpbCI6ImpvcmRhbkBleGFtcGxlLmNvbSJ9.C3MVjfmnul8dLNIgiv6Dt3jSefD07Y0QtDrOZ5oYSXo
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