generate_jwt

The generate_jwt statement is used to generate an RFC 7515-compliant JWT (JSON Web Token) which can be used, for example, for Google Cloud OAuth 2.0 Server to Server Authentication.

Syntax

generate_jwt keykey component1 [... componentN]asresult

Details

The generate_jwt statement performs the following actions:

• encodes all components as Base64URL

• concatenates all components using a dot separator (.)

• hashes the concatenated result using SHA256

• signs the hash with a provided PEM-encoded key using the RSA algorithm

• encodes the resulting signature as Base64URL

• builds JWT by concatenating the two results using a dot separator (.)

• stores the final result in th variable specified by the result parameter

The RSA key needs to be in PEM format. PEM format requires the header and footer to be on separate lines so it is important to separate the key contents with ${NEWLINE}as shown below:

var key = "-----BEGIN PRIVATE KEY-----${NEWLINE}Key-data-goes-here{$NEWLINE}-----END PRIVATE KEY-----"

Example

To acquire a Google Cloud OAuth 2.0 access token:

var private = "-----BEGIN PRIVATE KEY-----${NEWLINE}key goes here${NEWLINE}-----END PRIVATE KEY-----"
var email = "[e-mail]"
var url = "https://www.googleapis.com/oauth2/v4/token"
var scope = "https://www.googleapis.com/auth/cloud-platform"

var now = ${UNIX_UTC}
var expiry = (${now} + 3600)

var header = "{\"alg\":\"RS256\",\"typ\":\"JWT\"}"
var payload = "{\"iss\":\"${email}\",\"scope\":\"${scope}\",\"aud\":\"${url}\",\"iat\":\"${now}\",\"exp\":\"${expiry}\"}"

generate_jwt key ${private} ${header} ${payload} as JWT

# Make HTTP request according to https://developers.google.com/identity/protocols/OAuth2ServiceAccount
set http_header "Content-Type: application/x-www-form-urlencoded"
set http_body data "grant_type=urn%3Aietf%3Aparams%3Aoauth%3Agrant-type%3Ajwt-bearer&assertion=${JWT}"
buffer token = HTTP POST "${url}"

if (${HTTP_STATUS_CODE} != 200) {
	print Got HTTP status ${HTTP_STATUS_CODE}, expected a status of 200
	print The server response was:
	json format {token} 
	print {token}
	terminate
}

var access_token = $JSON{token}.[access_token]
print Access token: ${access_token}