Create code verifier and code challenge for OIDC Authorization Code Flow with PKCE in Java

OidcAuthCodeFlowWithPkce.java

package com.julianjupiter.oidc;

import java.nio.charset.StandardCharsets;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.util.Base64;

/**
 * @author Julian Jupiter
 */
public class OidcAuthCodeFlowWithPkce {
    public static String createCodeVerifier() {
        var secureRandom = new SecureRandom();
        var code = new byte[32];
        secureRandom.nextBytes(code);
        
        return Base64.getUrlEncoder()
                .withoutPadding()
                .encodeToString(code);
    }

    public static String createCodeChallenge(String verifier) throws NoSuchAlgorithmException {
        byte[] bytes = verifier.getBytes(StandardCharsets.US_ASCII);
        var messageDigest = MessageDigest.getInstance("SHA-256");
        messageDigest.update(bytes, 0, bytes.length);
        byte[] digest = messageDigest.digest();
        
        return Base64.getUrlEncoder()
                .withoutPadding()
                .encodeToString(digest);
    }
}

Sample.java

package com.julianjupiter.java.v21;

import java.security.NoSuchAlgorithmException;

import static com.julianjupiter.oidc.OidcAuthCodeFlowWithPkce.*;

/**
 * @author Julian Jupiter
 */
public class Sample {
    public static void main(String[] args) throws NoSuchAlgorithmException {
        String codeVerifier = createCodeVerifier();
        String codeChallenge = createCodeChallenge(codeVerifier);
        System.out.printf("Code verifier: %s%n", codeVerifier);
        System.out.printf("Code challenge: %s%n", codeChallenge);
    }
}