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Script to generate JWT for use with Github apps
#!/usr/bin/env bash
# Generate JWT for Github App
#
# Inspired by implementation by Will Haley at:
# http://willhaley.com/blog/generate-jwt-with-bash/
# From:
# https://stackoverflow.com/questions/46657001/how-do-you-create-an-rs256-jwt-assertion-with-bash-shell-scripting
thisdir="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
set -o pipefail
# Change these variables:
app_id=1337
app_private_key="$(< $thisdir/app.key)"
# Shared content to use as template
header='{
"alg": "RS256",
"typ": "JWT"
}'
payload_template='{}'
build_payload() {
jq -c \
--arg iat_str "$(date +%s)" \
--arg app_id "${app_id}" \
'
($iat_str | tonumber) as $iat
| .iat = $iat
| .exp = ($iat + 300)
| .iss = ($app_id | tonumber)
' <<< "${payload_template}" | tr -d '\n'
}
b64enc() { openssl enc -base64 -A | tr '+/' '-_' | tr -d '='; }
json() { jq -c . | LC_CTYPE=C tr -d '\n'; }
rs256_sign() { openssl dgst -binary -sha256 -sign <(printf '%s\n' "$1"); }
sign() {
local algo payload sig
algo=${1:-RS256}; algo=${algo^^}
payload=$(build_payload) || return
signed_content="$(json <<<"$header" | b64enc).$(json <<<"$payload" | b64enc)"
sig=$(printf %s "$signed_content" | rs256_sign "$app_private_key" | b64enc)
printf '%s.%s\n' "${signed_content}" "${sig}"
}
sign
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