how can I encode JWT with jmeter - jmeter

Question

this is my payload
field1=valueField1&field2=valueField2&request=jwtEncodedRequest
Where jwtEncodedRequest is indeed a request encoded via jwt.
currently I'm using jwt.io to create an encoded request.
is it possible automatize this with jmeter?

Answer 1

Yes you can:
Use a JSR223 PreProcessor with Groovy
Compute token using this java library
Add the above library to jmeter/lib folder

Answer 2

Add Apache Ivy jar to JMeter Classpath
Restart JMeter to pick the .jar up
Add JSR223 Sampler to your Test Plan
Put the following code to "Script" area:
#Grab(group='io.jsonwebtoken', module='jjwt', version='0.9.1')
import io.jsonwebtoken.*
import java.security.PrivateKey
import java.util.Base64
import java.util.Base64.Decoder
import java.nio.charset.StandardCharsets
import java.security.interfaces.ECPrivateKey
import java.security.KeyFactory
import java.security.NoSuchAlgorithmException
import java.security.spec.PKCS8EncodedKeySpec
// Generating Tokens for API Requests
// https://developer.apple.com/documentation/appstoreconnectapi/generating_tokens_for_api_requests
def exp = (System.currentTimeMillis() / 1000 + 1200).intValue()
//20 minutes from now
//JWT Payload (update with your Issuer ID)
String jsonString = """{"iss":"57246542-96fe-1a63-e053-0824d011072a","exp":${exp},"aud":"appstoreconnect-v1"}""";
//Content of the AuthKey_2X9R4HXF34.p8
/*
-----BEGIN PRIVATE KEY-----
MIGTAgEAMBMGByqGSM49AgEGCCqGSM49AwEHBHkwdwIBAQQg74+aaeYnqEIewDn8
Xh0rQXaQqAHSLGDyL9fV0p1hhxGgCgYIKoZIzj0DAQehRANCHOTEUjCMi4Vt7JGZ
jsRP1zF765oerCqfvHZYGqSeJl8AmK0awchcqAaMlw7hROoA2MToqx+llo2p9lZC
QYbeerau
-----END PRIVATE KEY-----
*/
//Key concatenated in a single line
//You better not hard code this key
def base64EncodedPrivateKey = "MIGTAgEAMBMGByqGSM49AgEGCCqGSM49AwEHBHkwdwIBAQQg74+aaeYnqEIewDn8Xh0rQXaQqAHSLGDyL9fV0p1hhxGgCgYIKoZIzj0DAQehRANCHOTEUjCMi4Vt7JGZjsRP1zF765oerCqfvHZYGqSeJl8AmK0awchcqAaMlw7hROoA2MToqx+llo2p9lZCQYbeerau"
ECPrivateKey signingKey
Base64.Decoder dec= Base64.getDecoder();
keyBytes = dec.decode(base64EncodedPrivateKey.getBytes(StandardCharsets.US_ASCII));
PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(keyBytes);
KeyFactory keyFactory = KeyFactory.getInstance("EC");
signingKey = keyFactory.generatePrivate(keySpec);
//Notice you don't need to encode the header nor the payload
String jwtToken = Jwts.builder()
//JWT Header
.setHeaderParam("typ","JWT")
.setHeaderParam("alg","ES256")
.setHeaderParam("kid","2X9R4HXF34") //UPDATE with your Key Identifier
.setPayload(jsonString)
.signWith(SignatureAlgorithm.ES256, signingKey)
.compact();
log.info(jwtToken)
You should see JWT token printed to jmeter.log file:
More information:
JSON Web Token Quickstart
Apache Groovy - Why and How You Should Use It