Technical Solutions: 2025

Thursday, 9 October 2025

Spring security interview question.

🧩 1. Core Spring Security Architecture

Q1. What are the main components of Spring Security?
Q2. Explain the Spring Security filter chain and how it works internally.
Q3. What is the difference between FilterChainProxy and DelegatingFilterProxy?
Q4. How does Spring Security integrate with the Servlet container?
Q5. What is the role of SecurityContext and SecurityContextHolder?

🔐 2. Authentication & Authorization

Q6. Explain the authentication flow in Spring Security.
Q7. What is the difference between AuthenticationManager and AuthenticationProvider?
Q8. How does Spring Security handle authorization decisions?
Q9. What is the purpose of AccessDecisionManager and AccessDecisionVoter?
Q10. How do you customize authentication (e.g., using database, LDAP, JWT, or OAuth)?

💾 3. JWT (JSON Web Token) & Stateless Authentication

Q11. Explain how JWT-based authentication works in Spring Security.
Q12. What are the pros and cons of using JWT vs session-based authentication?
Q13. How do you implement token invalidation (logout) in JWT-based systems?
Q14. How can you refresh JWT tokens securely?
Q15. How would you prevent token replay attacks?

🧰 4. Configuration Approaches

Q16. What’s the difference between WebSecurityConfigurerAdapter and the new SecurityFilterChain approach (Spring Security 5.7+)?
Q17. How do you configure multiple HttpSecurity instances for different API paths?
Q18. How would you disable security for a specific endpoint (e.g., /health, /actuator)?
Q19. How to secure REST APIs using Spring Security annotations (@PreAuthorize, @Secured)?
Q20. Explain method-level vs URL-level security.

⚙️ 5. Customization & Extensibility

Q21. How do you create a custom authentication filter?
Q22. How do you plug in a custom UserDetailsService?
Q23. Explain how to add custom claims to JWT during login.
Q24. How do you handle multi-factor authentication (MFA) in Spring Security?
Q25. How can you secure microservices communicating over REST (e.g., internal JWT validation)?

🧠 6. Advanced Concepts

Q26. Explain SecurityContextPersistenceFilter and its purpose.
Q27. What is AnonymousAuthenticationFilter and when does it come into play?
Q28. How does Spring Security handle CSRF protection in REST APIs?
Q29. Explain how CORS and Spring Security interact.
Q30. What are stateless sessions, and how are they configured?

🧩 7. OAuth2 / OpenID Connect

Q31. Explain the OAuth2 authorization code flow.
Q32. What are the key differences between OAuth2 and OpenID Connect?
Q33. How would you secure a resource server and client application using Spring Security OAuth2?
Q34. What’s the difference between BearerTokenAuthenticationFilter and BasicAuthenticationFilter?
Q35. How do you refresh access tokens securely in OAuth2?

🧱 8. Security Best Practices

Q36. How do you prevent brute-force attacks in Spring Security?
Q37. How do you implement rate-limiting or IP-based blocking?
Q38. How do you store passwords securely in the database?
Q39. What are common security misconfigurations you’ve seen in Spring projects?
Q40. How do you secure WebSockets with Spring Security?

☁️ 9. Real-World & Integration

Q41. How would you design authentication for a microservices architecture (e.g., using JWT + Redis)?
Q42. How can you propagate authentication across multiple services (SSO)?
Q43. How to integrate Spring Security with AWS Cognito or Azure AD?
Q44. How do you secure actuator endpoints in production?
Q45. How do you test secured endpoints using JUnit and Mockito?

🧪 10. Troubleshooting & Debugging

Q46. How do you debug 403 Forbidden issues in Spring Security?
Q47. How do you log authentication and authorization events?
Q48. How do you verify your filter order in the Spring Security chain?
Q49. What’s the difference between @WithMockUser and @WithUserDetails in testing?
Q50. How would you profile or optimize security filters for performance?

✅ Bonus: Scenario-Based Questions

You need to allow multiple concurrent logins per user, but also support logout from all sessions — how do you implement it?
You want to support JWT authentication but also allow API key-based access for internal systems — how would you design it?
You want to cache user roles and permissions to avoid frequent DB hits — how would you do that securely?
You want to secure communication between two Spring Boot microservices — what’s your approach (TLS, JWT, OAuth2)?
How would you audit who accessed which endpoint and when?

Would you like me to create a PDF or a structured study sheet (with answers and diagrams for each topic like JWT, filter chain, etc.)?
It’s perfect for 10+ yrs Spring Security interview prep.

Friday, 3 October 2025

How to Create a Pure Java Service-Layer JAR from a Spring Boot Project

When working on a Spring Boot application, the service layer often contains the business logic that you may want to reuse in other projects. But what if you want to create a JAR of only the service layer and use it in a plain Java project without any Spring dependencies? This guide walks you through the process step by step.

Why Separate the Service Layer?

Separating the service layer into its own module or project has several advantages:

Reusability: You can use it in multiple applications, including plain Java apps.
Decoupling: Keeps business logic separate from controllers or web-specific code.
Simpler Testing: Service logic can be tested independently of web or Spring Boot context.

Step 1: Remove Spring Dependencies

Spring annotations like @Service, @Component, @Autowired, or @Transactional won’t work in a plain Java application because they rely on Spring’s dependency injection and application context.

You need to:

Remove all Spring annotations.
Replace @Autowired dependencies with constructor or setter injection.
Handle transactions manually if needed.

Before (Spring Boot Service):

@Service

public class MyService {

@Autowired

private MyRepository repo;

@Transactional

public void doSomething() {

repo.saveData();

}

After (Plain Java Service):

public class MyService {

private final MyRepository repo;

public MyService(MyRepository repo) {

this.repo = repo;

}

public void doSomething() {

repo.saveData();

}

Step 2: Prepare the Service Layer Module

Organize your project into a separate module for the service layer. Example structure:

my-app

│

├─ service-layer <-- This will become the JAR

│ └─ src/main/java/... (all service classes)

│ └─ pom.xml

│

├─ web-layer <-- Spring Boot app (controllers)

│ └─ src/main/java/...

│ └─ pom.xml

│

└─ pom.xml <-- parent pom

Step 3: Create a Minimal `pom.xml`

Since you don’t want any Spring dependency, the pom.xml is very simple:

<groupId>com.example</groupId>

<artifactId>service-layer</artifactId>

</dependencies>

</project>

Only include libraries like JDBC drivers, Redis client, or other third-party APIs if your service uses them.

Step 4: Build the JAR

From the service-layer module folder, run:

mvn clean install

service-layer/target/service-layer-1.0.0.jar

This JAR now contains only your service layer and no controllers or Spring Boot classes.

Step 5: Use the JAR in a Plain Java Application

Add the JAR to your Java project classpath (or as a Maven dependency if installed in the local repo) and use it like any normal Java library:

public class Main {

public static void main(String[] args) {

MyRepository repo = new MyRepository();

MyService service = new MyService(repo);

service.doSomething();

}

No Spring required, everything works in pure Java.

Key Takeaways

Spring annotations do nothing in a plain Java app. To use your service layer outside Spring Boot, remove them.
Use constructor or setter injection to manage dependencies manually.
Keep only necessary dependencies in the service-layer pom.xml to make it lightweight.
Build as a JAR using Maven and reuse it anywhere, including plain Java projects.

This approach allows you to decouple your business logic from Spring, making your service layer reusable, lightweight, and independent of any specific framework.

Stream Concat example

https://www.netjstech.com/2022/01/java-stream-concat-with-examples.html

//code for fetch user assigned Specific design group
Long[] designGroupAssignedToUser = this.getDesignGroupBuUserId(user);
designGroupIds = Stream.concat(
                Arrays.stream(Optional.ofNullable(designGroupIds).orElse(new Long[0])),
                Arrays.stream(Optional.ofNullable(designGroupAssignedToUser).orElse(new Long[0]))
        )
        .distinct()
        .toArray(Long[]::new);
//end of code

Tuesday, 23 September 2025

Multithreading practical example

https://github.com/xlciela/learn-multi-threading/tree/main/java

Wednesday, 10 September 2025

Runnable ,callable ,Executer service Thred example

import java.util.concurrent.Callable;

import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

public class RunnableAndThread implements Runnable , Callable<Integer> {
    @Override
    public void run() {
        System.out.println("hello");
    }

    public void myrun() {
        System.out.println("hellopawan");
    }
    @Override
    public Integer call() {
        return 50;
    }

    public static void main(String args[]) throws ExecutionException, InterruptedException {
        ExecutorService executor = Executors.newFixedThreadPool(3);
        executor.submit((Runnable) new RunnableAndThread());
        executor.submit(()->new RunnableAndThread().myrun());
        Future<Integer> future = executor.submit((Callable<Integer>) new RunnableAndThread());
        System.out.println("Callable result: " + future.get());
        //Thread runnableAndThread = new Thread(()->new RunnableAndThread().myrun());
        //runnableAndThread.start();
        //Thread runnableAndThread1 = new Thread(new RunnableAndThread());
        //runnableAndThread1.start();
    }
}

Tuesday, 5 August 2025

Amazon SES RAW email

https://docs.aws.amazon.com/ses/latest/dg/send-email-raw.html

package com.amazonaws.samples;

import java.io.ByteArrayOutputStream;

import java.io.IOException;

import java.io.PrintStream;

import java.nio.ByteBuffer;

import java.util.Properties;

// JavaMail libraries. Download the JavaMail API

// from https://javaee.github.io/javamail/

import javax.activation.DataHandler;

import javax.activation.DataSource;

import javax.activation.FileDataSource;

import javax.mail.Message;

import javax.mail.MessagingException;

import javax.mail.Session;

import javax.mail.internet.AddressException;

import javax.mail.internet.InternetAddress;

import javax.mail.internet.MimeBodyPart;

import javax.mail.internet.MimeMessage;

import javax.mail.internet.MimeMultipart;

// AWS SDK libraries. Download the AWS SDK for Java

// from https://aws.amazon.com/sdk-for-java

import com.amazonaws.regions.Regions;

import com.amazonaws.services.simpleemail.AmazonSimpleEmailService;

import com.amazonaws.services.simpleemail.AmazonSimpleEmailServiceClientBuilder;

import com.amazonaws.services.simpleemail.model.RawMessage;

import com.amazonaws.services.simpleemail.model.SendRawEmailRequest;

public class AmazonSESSample {

// Replace sender@example.com with your "From" address.

// This address must be verified with Amazon SES.

private static String SENDER = "Sender Name <sender@example.com>";

// Replace recipient@example.com with a "To" address. If your account

// is still in the sandbox, this address must be verified.

private static String RECIPIENT = "recipient@example.com";

// Specify a configuration set. If you do not want to use a configuration

// set, comment the following variable, and the

// ConfigurationSetName=CONFIGURATION_SET argument below.

private static String CONFIGURATION_SET = "ConfigSet";

// The subject line for the email.

private static String SUBJECT = "Customer service contact info";

// The full path to the file that will be attached to the email.

// If you're using Windows, escape backslashes as shown in this variable.

private static String ATTACHMENT = "C:\\Users\\sender\\customers-to-contact.xlsx";

// The email body for recipients with non-HTML email clients.

private static String BODY_TEXT = "Hello,\r\n"

+ "Please see the attached file for a list "

+ "of customers to contact.";

// The HTML body of the email.

private static String BODY_HTML = "<html>"

+ "<head></head>"

+ "<body>"

+ "<h1>Hello!</h1>"

+ "<p>Please see the attached file for a "

+ "list of customers to contact.</p>"

+ "</body>"

+ "</html>";

public static void main(String[] args) throws AddressException, MessagingException, IOException {

Session session = Session.getDefaultInstance(new Properties());

// Create a new MimeMessage object.

MimeMessage message = new MimeMessage(session);

// Add subject, from and to lines.

message.setSubject(SUBJECT, "UTF-8");

message.setFrom(new InternetAddress(SENDER));

message.setRecipients(Message.RecipientType.TO, InternetAddress.parse(RECIPIENT));

// Create a multipart/alternative child container.

MimeMultipart msg_body = new MimeMultipart("alternative");

// Create a wrapper for the HTML and text parts.

MimeBodyPart wrap = new MimeBodyPart();

// Define the text part.

MimeBodyPart textPart = new MimeBodyPart();

textPart.setContent(BODY_TEXT, "text/plain; charset=UTF-8");

// Define the HTML part.

MimeBodyPart htmlPart = new MimeBodyPart();

htmlPart.setContent(BODY_HTML,"text/html; charset=UTF-8");

// Add the text and HTML parts to the child container.

msg_body.addBodyPart(textPart);

msg_body.addBodyPart(htmlPart);

// Add the child container to the wrapper object.

wrap.setContent(msg_body);

// Create a multipart/mixed parent container.

MimeMultipart msg = new MimeMultipart("mixed");

// Add the parent container to the message.

message.setContent(msg);

// Add the multipart/alternative part to the message.

msg.addBodyPart(wrap);

// Define the attachment

MimeBodyPart att = new MimeBodyPart();

DataSource fds = new FileDataSource(ATTACHMENT);

att.setDataHandler(new DataHandler(fds));

att.setFileName(fds.getName());

// Add the attachment to the message.

msg.addBodyPart(att);

// Try to send the email.

try {

System.out.println("Attempting to send an email through Amazon SES "

+"using the AWS SDK for Java...");

// Instantiate an Amazon SES client, which will make the service

// call with the supplied AWS credentials.

AmazonSimpleEmailService client =

AmazonSimpleEmailServiceClientBuilder.standard()

// Replace US_WEST_2 with the AWS Region you're using for

// Amazon SES.

.withRegion(Regions.US_WEST_2).build();

// Print the raw email content on the console

PrintStream out = System.out;

message.writeTo(out);

// Send the email.

ByteArrayOutputStream outputStream = new ByteArrayOutputStream();

message.writeTo(outputStream);

RawMessage rawMessage =

new RawMessage(ByteBuffer.wrap(outputStream.toByteArray()));

SendRawEmailRequest rawEmailRequest =

new SendRawEmailRequest(rawMessage)

.withConfigurationSetName(CONFIGURATION_SET);

client.sendRawEmail(rawEmailRequest);

System.out.println("Email sent!");

// Display an error if something goes wrong.

} catch (Exception ex) {

System.out.println("Email Failed");

System.err.println("Error message: " + ex.getMessage());

ex.printStackTrace();

}

Thursday, 10 July 2025

Spring bean configuration with xml and java

If you want o use spring bean configuration with xml then you have to create bean.xml file

Monday, 30 June 2025

Revert a Specific File Committed that Pushed to Remote Git

You want to undo changes to just one file, even though the commit has already been pushed.

Option 1: Revert the file to the previous version and commit again (Safe & Recommended)

-----------------------------------------------------------------------

1. Revert the file to the version from the previous commit:

git checkout HEAD^ -- path/to/your/file

2. Stage the reverted file:

git add path/to/your/file

3. Commit the change:

git commit -m "Revert file to previous version"

4. Push to remote:

git push

Tip: You can use a specific commit hash instead of HEAD^

Option 2: Reset file to a specific older commit version (Safe if targeted)

------------------------------------------------------------

1. View commit history for the file:

git log path/to/file

2. Reset the file to that commit's version:

git checkout <commit-hash> -- path/to/file

3. Commit and push:

git add path/to/file

git commit -m "Revert file to specific commit version"

git pushOption 3: Revert the whole commit (only if the commit changed only this file)

-----------------------------------------------------------

git revert <commit-hash>

git push

Avoid:

------

Avoid using 'git reset --hard' and 'git push -f' on shared branches.

Always use a clean commit to revert individual file changes on shared remotes.

Friday, 30 May 2025

My sql do alter table on production -Percona's

pt-online-schema-change \

--alter "ADD INDEX idx_project_doc_filter (

external_app_id,

user_id,

date_created DESC,

design_name,

subject_folder_id,

listing_id,

date_updated

)" \

--user=your_user \

--password=your_pass \

--host=your_host \

--execute

Friday, 9 May 2025

spring swagger documentation

https://springdoc.org/

<dependency> <groupId>org.springdoc</groupId> <artifactId>springdoc-openapi-starter-webmvc-ui</artifactId> <version>2.5.0</version> </dependency>

Monday, 5 May 2025

functional interface

Thursday, 10 April 2025

AWS credential provider types

Provider	Use Case	Notes
`StaticCredentialsProvider`	Manual credentials	Don't use in production
`EnvironmentVariableCredentialsProvider`	Env vars	Good for local/prod
`SystemPropertyCredentialsProvider`	JVM properties	Useful in CI/CD
`ProfileCredentialsProvider`	Named profiles in AWS config files	Great for multi-account setups
`DefaultCredentialsProvider`	Let AWS figure it out	👍 Preferred way
`InstanceProfileCredentialsProvider`	IAM role on EC2	Secure and scalable
`ContainerCredentialsProvider`	IAM role on ECS/EKS	Works well in containers

Tuesday, 8 April 2025

Maelstrom

1.Makefile

2.Maelstrom

3.ibets

4.jdbi

5.bazel

Thursday, 20 March 2025

Use velocity template in spring 5

Step 1

@Configuration

public class VelocityConfig {

@Bean

public VelocityEngine velocityEngine() {

Properties properties = new Properties();

properties.setProperty(RuntimeConstants.RESOURCE_LOADER, "classpath");

properties.setProperty("classpath.resource.loader.class", ClasspathResourceLoader.class.getName());

VelocityEngine velocityEngine = new VelocityEngine();

velocityEngine.init(properties);

return velocityEngine;

}

Step 2

public class VelocityTemplateProcessor {

private final VelocityEngine velocityEngine;

public VelocityTemplateProcessor(VelocityEngine velocityEngine) {

this.velocityEngine = velocityEngine;

}

public String processTemplate(String templateName, Map<String, Object> model) {

Template template = velocityEngine.getTemplate(templateName);

VelocityContext context = new VelocityContext(model);

StringWriter writer = new StringWriter();

template.merge(context, writer);

return writer.toString(); // Return final processed content

}

Step 3

@RestController

public class MyController {

private final VelocityTemplateProcessor velocityProcessor;

public MyController(VelocityTemplateProcessor velocityProcessor) {

this.velocityProcessor = velocityProcessor;

}

@GetMapping("/welcome")

public String generateWelcomeMessage() {

Map<String, Object> model = new HashMap<>();

model.put("username", "Pawan");

return velocityProcessor.processTemplate("templates/welcome.vm", model);

}

step 4

Located in src/main/resources/templates/welcome.vm:

perl

Monday, 10 March 2025

Code push learnig

Read code before push.

Remove unwanted imports.

Take your time to push code and in hurry.

Wednesday, 5 March 2025

maelstromapp

https://maelstromapp.com/docs/event_sources/aws_sqs/

Friday, 21 February 2025

single-click unssubs cribe

To set a One-Click Unsubscribe Header in an SMTPMessage and define an API endpoint for handling unsubscribes, you need to use custom headers in JavaMail.

📌 Steps to Add One-Click Unsubscribe Headers

Set the standard List-Unsubscribe header
- This allows email clients to display an "Unsubscribe" button.
Set the List-Unsubscribe-Post header (for one-click unsubscribe)
- Required for Gmail, Yahoo, and other email providers.
Use an API endpoint (POST method) to handle unsubscriptions.

✅ Implementation

java
import javax.mail.*;
import javax.mail.internet.*;
import java.util.Properties;

public class OneClickUnsubscribeEmail {
    public static void main(String[] args) {
        final String smtpHost = "smtp.example.com"; // SMTP Server
        final String fromEmail = "sender@example.com";
        final String toEmail = "recipient@example.com";
        final String unsubscribeUrl = "https://example.com/unsubscribe?email=" + toEmail;
        final String unsubscribeApiUrl = "https://example.com/api/unsubscribe";

        Properties properties = new Properties();
        properties.put("mail.smtp.host", smtpHost);
        properties.put("mail.smtp.auth", "true");
        properties.put("mail.smtp.starttls.enable", "true");

        Session session = Session.getInstance(properties, new Authenticator() {
            protected PasswordAuthentication getPasswordAuthentication() {
                return new PasswordAuthentication("your-username", "your-password");
            }
        });

        try {
            SMTPMessage message = new SMTPMessage(session);
            message.setFrom(new InternetAddress(fromEmail));
            message.setRecipients(Message.RecipientType.TO, InternetAddress.parse(toEmail));
            message.setSubject("One-Click Unsubscribe Test");
            message.setText("Hello, this is a test email with a one-click unsubscribe link.");

            // 📌 1️⃣ Add `List-Unsubscribe` Header (Clickable Unsubscribe Button in Email Clients)
            message.setHeader("List-Unsubscribe", "<" + unsubscribeUrl + ">, <mailto:unsubscribe@example.com>");

            // 📌 2️⃣ Add `List-Unsubscribe-Post` Header (One-Click Unsubscribe via API)
            message.setHeader("List-Unsubscribe-Post", "List-Unsubscribe=One-Click");

            // 📌 3️⃣ Add `List-Unsubscribe` API Endpoint
            message.setHeader("List-Unsubscribe", "<" + unsubscribeApiUrl + ">");

            // Send the message
            Transport.send(message);
            System.out.println("Email sent successfully with one-click unsubscribe header!");

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

📌 Explanation

List-Unsubscribe Header

Provides an unsubscribe URL and a mailto option.
Some email clients (e.g., Gmail, Outlook) will show an unsubscribe button.

java
message.setHeader("List-Unsubscribe", "<https://example.com/unsubscribe?email=recipient@example.com>, <mailto:unsubscribe@example.com>");

List-Unsubscribe-Post Header
- Allows email providers to send a POST request to your API for one-click unsubscribe.
```
java
message.setHeader("List-Unsubscribe-Post", "List-Unsubscribe=One-Click");
```

List-Unsubscribe with API Endpoint

Some email providers use this URL for direct API calls.

java
message.setHeader("List-Unsubscribe", "<https://example.com/api/unsubscribe>");

📌 How Does It Work?

Gmail/Yahoo users will see an "Unsubscribe" button in their email client.
Clicking it will automatically trigger an API request to https://example.com/api/unsubscribe to unsubscribe the user.
If the email client does not support one-click unsubscribe, the user can still click the manual link.

🚀 Final Thoughts

✅ Supports Gmail, Yahoo, Outlook, etc.
✅ Improves email deliverability (avoids spam folder)
✅ Ensures compliance with anti-spam laws (e.g., GDPR, CAN-SPAM)

Would you like help setting up the unsubscribe API? 🚀

final String unsubscribeUrl \= "https://example.com/unsubscribe?email=" + toEmail; final String unsubscribeApiUrl \= "https://example.com/api/unsubscribe";

why we useing two urls hare what is is the use of unsubscribeApiUrl

Why Are There Two Unsubscribe URLs?

In the email header, we are using two different unsubscribe URLs for different purposes:

unsubscribeUrl (User-Friendly Web Link)
- This is a clickable link that redirects the user to a webpage where they can manually unsubscribe.
- Example:
```
perl
List-Unsubscribe: <https://example.com/unsubscribe?email=user@example.com>, <mailto:unsubscribe@example.com>
```
- This is useful because some users might want to see an unsubscribe page before confirming.
unsubscribeApiUrl (Automated One-Click API Endpoint)
- This is used for automatic one-click unsubscription via email providers like Gmail and Yahoo.
- Example:
```
mathematica
List-Unsubscribe: <https://example.com/api/unsubscribe>
List-Unsubscribe-Post: List-Unsubscribe=One-Click
```
- When a user clicks the "Unsubscribe" button in Gmail/Yahoo, the email provider sends an HTTP POST request to this API, unsubscribing the user without requiring any further action.

📌 Summary of Their Uses

Unsubscribe URL	Purpose	Who Uses It?
`unsubscribeUrl` (`https://example.com/unsubscribe?email=user@example.com`)	Redirects users to a webpage where they can manually unsubscribe.	Users who click the "Unsubscribe" link in the email.
`unsubscribeApiUrl` (`https://example.com/api/unsubscribe`)	One-click unsubscribe API (Gmail/Yahoo will send a `POST` request to this URL).	Email providers (Gmail, Yahoo) when a user clicks "Unsubscribe" in their email client.

🚀 How Does It Work in Real Life?

User clicks "Unsubscribe" in Gmail.
Gmail sends a POST request to https://example.com/api/unsubscribe.
The server automatically unsubscribes the user without any confirmation.
If the user clicks the manual unsubscribe link, they visit https://example.com/unsubscribe?email=user@example.com and can confirm before unsubscribing.

🚀 Why Is This Important?

✅ Improves email deliverability → Reduces spam complaints.
✅ Complies with CAN-SPAM & GDPR → Provides an easy opt-out.
✅ Better user experience → One-click unsubscribes for email providers, but also a manual option for users.

Would you like help implementing the API endpoint (unsubscribeApiUrl) to handle the one-click unsubscribe? 🚀