Step 1

import com.nimbusds.*;
import org.json.JSONObject;


// The authorization endpoint of E-Consent 
URI authorizationEndpoint = new URI("https://e-consent-preprod1.nets.eu/e-consent/authorize");

// The client identifier (has to be pre-registered)
ClientID clientId = new ClientID("myinsuranse.com");

// The client redirect URI which has to be pre-registered with the ACS
URI redirectURI = new URI("https://myinsurance.com/consent/callback");

// Always 'code'
ResponseType responseType = new ResponseType(ResponseType.Value.CODE);

// Should be 'consent' or 'login' based on whether the scope 'offline_access' is set
String prompt = "login";

// A random generated state (string) used for pairing the response to the request
State state = new State(generateRandomString());

// A globally unique generated nonce
String nonce = generateRandomString();

// The id of the requested scope (not an actual web page)
Scope scope = new Scope("https://myinsurance.com/api/get-insurance-documents");

// The name of the token expected in return
String tokenName = "myinsurance-token";

// Data dynamically included in the consent statement. For instance the third party that the consent is given to.
String thirdParty = "InstantInsurance.com";

// The electronic ID to use for authentication
String eID = "NO_BANKID_MOB";


// Build the content of the 'request' parameter
JWTClaimsSet claims = new JWTClaimsSet.Builder()
        .claim("response_type", responseType.toString())
        .claim("client_id", clientId.toString())
        .claim("redirect_uri", redirectURI.toString())
        .claim("scope", scope.toString())
        .claim("state", state)
        .claim("nonce", nonce)
        .claim("prompt", prompt)
        .claim("amr", eID)
        .claim("claims", new JSONObject()
                .put(tokenName, new JSONObject()
                        .put("thirdparty", thirdParty)) 
                .toString())
        .build();

// Sign the JWT with the client private key
SignedJWT requestJWT = new SignedJWT(new JWSHeader(JWSAlgorithm.RS256), claims);
requestJWT.sign(new RSASSASigner(getPrivateKey()));

// Build the request
AuthorizationRequest authenticationRequest = new AuthorizationRequest.Builder(
        responseType, clientId)
        .endpointURI(authorizationEndpoint)
        .redirectionURI(redirectURI)
        .scope(scope)
        .state(state)
        .customParameter("request", requestJWT.serialize())
        .customParameter("prompt", prompt)
        .customParameter("nonce", nonce)
        .build();

URI requestURI = authenticationRequest.toURI();