Bash JWT Encoder

jwtencoder.sh

#!/usr/bin/env bash

#
# JWT Encoder Bash Script
#

secret='SOME SECRET'

# Static header fields.
header='{
    "typ": "JWT",
    "alg": "HS256",
    "kid": "0001",
    "iss": "Bash JWT Generator"
}'

# Use jq to set the dynamic `iat` and `exp`
# fields on the header using the current time.
# `iat` is set to now, and `exp` is now + 1 second.
header=$(
    echo "${header}" | jq --arg time_str "$(date +%s)" \
    '
    ($time_str | tonumber) as $time_num
    | .iat=$time_num
    | .exp=($time_num + 1)
    '
)
payload='{
    "Id": 1,
    "Name": "Hello, world!"
}'

base64_encode()
{
    declare input=${1:-$(</dev/stdin)}
    # Use `tr` to URL encode the output from base64.
    printf '%s' "${input}" | base64 | tr -d '=' | tr '/+' '_-' | tr -d '\n'
}

json() {
    declare input=${1:-$(</dev/stdin)}
    printf '%s' "${input}" | jq -c .
}

hmacsha256_sign()
{
    declare input=${1:-$(</dev/stdin)}
    printf '%s' "${input}" | openssl dgst -binary -sha256 -hmac "${secret}"
}

header_base64=$(echo "${header}" | json | base64_encode)
payload_base64=$(echo "${payload}" | json | base64_encode)

header_payload=$(echo "${header_base64}.${payload_base64}")
signature=$(echo "${header_payload}" | hmacsha256_sign | base64_encode)

echo "${header_payload}.${signature}"

Taken from https://willhaley.com/blog/generate-jwt-with-bash/, for posterity.

encoder returns error when using empty payload
payload='{}'

+++ openssl dgst -binary -sha256 -hmac GCBsn2MC8KBBcocP26NasH2K3bvDMDSW7wYXayrDv5xUp49IQ24Q
test.sh: line 21: warning: command substitution: ignored null byte in input
�"Z��*�ko��+'input=])�c�`�
            ����'
�"Z��*�ko��+s '])�c�`�
            ����'

encoder returns error when using empty payload payload='{}'

+++ openssl dgst -binary -sha256 -hmac GCBsn2MC8KBBcocP26NasH2K3bvDMDSW7wYXayrDv5xUp49IQ24Q
test.sh: line 21: warning: command substitution: ignored null byte in input
�"Z��*�ko��+'input=])�c�`�
            ����'
�"Z��*�ko��+s '])�c�`�
            ����'

#!/bin/bash
token_gen() {
    secret=$1
    header='{
        "typ": "JWT",
        "alg": "HS256",
        "kid": "0001",
        "iss": "Bash JWT Generator"
    }'
    header=$(
        echo "${header}" | jq --arg time_str "$(date +%s)" \
        '
        ($time_str | tonumber) as $time_num
        | .iat=$time_num
        | .exp=($time_num + 1)
        '
    )
    payload='{}'
    #shellcheck disable=2120
    base64_encode() {
        declare input=${1:-$(</dev/stdin)}
        printf '%s' "${input}" | base64 | tr -d '=' | tr '/+' '_-' | tr -d '\n'
    }
    #shellcheck disable=2120
    json() {
        declare input=${1:-$(</dev/stdin)}
        printf '%s' "${input}" | jq -c .
    }
    #shellcheck disable=2120
    hmacsha256_sign() {
        declare input=${1:-$(</dev/stdin)}
        printf '%s' "${input}" | openssl dgst -binary -sha256 -hmac "${secret}"
    }
    header_base64=$(echo "${header}" | json | base64_encode)
    payload_base64=$(echo "${payload}" | json | base64_encode)
    #shellcheck disable=2116
    header_payload=$(echo "${header_base64}.${payload_base64}")
    signature=$(echo "${header_payload}" | hmacsha256_sign | base64_encode)
    echo "${header_payload}.${signature}"
}

SECRET_KEY=GCBsn2MC8KBBcocP26NasH2K3bvDMDSW7wYXayrDv5xUp49IQ24Q
AUTH_TOKEN=$(token_gen "$SECRET_KEY")
echo $AUTH_TOKEN