You may try writing a custom java code in pyInvokeRest connector and  implement the HS256 API’s from  https://connect2id.com/products/nimbus-jose-jwt .

JWSObject jwsObject = new JWSObject(new JWSHeader(JWSAlgorithm.HS256),

                                    new Payload("Hello, world!"));

// We need a 256-bit key for HS256 which must be pre-shared

byte[] sharedKey = new byte[32];

new SecureRandom().nextBytes(sharedKey);

// Apply the HMAC to the JWS object

jwsObject.sign(new MACSigner(sharedKey));

// Output to URL-safe format

jwsObject.serialize();

Thanks,

Arun

I also had the same problem as a external service required a HMac signed token. It's already time ago whe this quetion has been raised, but for the sec of somebody needs a complete solution.

This is a complete code which you can copy into a function rule and is should work immediately.

You need to include the following packages in your library which you will use for the fuction rule:

java.util.*

com.nimbusds.jwt.*

com.nimbusds.jose.*

com.nimbusds.jose.crypto.*

/* Code Block START*/

JWSObject signedJWT = null;

try{

  // Create the JSON JWT Header

  JWSHeader header = new JWSHeader(JWSAlgorithm.HS256);

  

  // add expiration time (in milliseconds)

  long expL =  new Date().getTime();

  expL = expL+90000;

  // Create the JSON JWT Payload

  JWTClaimsSet claimsSet = new JWTClaimsSet.Builder()

    .subject("/your Subject")

    .expirationTime(new Date(expL))

    .issueTime(new Date())

    .issuer("yourIssuer")

    .jwtID(key)

    .claim("uid", "some claims you want") // append as much as you want before calling build(), like .claim("","").claim("","") as the return is always the builder object.

    .build();

  signedJWT = new SignedJWT( header, claimsSet );

  // Sign with the HS256 key passed as the string parameter

  signedJWT.sign( new MACSigner(key.getBytes()) );

  

}

catch ( Exception e )

{

  oLog.infoForced("CustomUtils generate Token with HMac: " + e.getMessage() );

  return "";

}

return signedJWT.serialize();

/* Code Block END*/