1. Introduction

In this tutorial, we will cover how to set up user authentication and roles in MongoDB. Authentication is a critical aspect of any application development as it ensures that your data is secure and accessible only to authorized users. Roles, on the other hand, define what actions a user can perform, ensuring data integrity and security.

Here's what you will learn:
- How to create users in MongoDB
- How to assign roles to users
- How to authenticate users using MongoDB

Prerequisites:
- Basic understanding of MongoDB
- MongoDB installed on your machine

2. Step-by-Step Guide

Creating a User

To create a user, we use the db.createUser() method. This method takes in a document that defines the user's username, password, and roles.

db.createUser(
  {
    user: "testUser",
    pwd: "testPassword",
    roles: [ "readWrite", "dbAdmin" ]
  }
)

Assigning Roles

Roles define what actions a user can perform. MongoDB provides built-in roles that can be assigned to a user. Examples of these roles include read, readWrite, and dbAdmin.

Authenticating a User

To authenticate a user, we use the db.auth() method. This method takes in the username and password of the user as parameters.

db.auth("testUser", "testPassword")

3. Code Examples

Creating a User with readWrite Role

db.createUser(
  {
    user: "testUser",
    pwd: "testPassword",
    roles: [ "readWrite" ]
  }
)

In the above code snippet:
- testUser is the username
- testPassword is the password
- readWrite is the role assigned to the user

This will create a user with readWrite role.

Authenticating a User

db.auth("testUser", "testPassword")

In the above code snippet:
- testUser is the username
- testPassword is the password

This will authenticate the user and return 1 if successful, else 0.

4. Summary

In this tutorial, we learned how to create users in MongoDB, assign roles to them, and authenticate them. We also learned about the built-in roles in MongoDB.

Next steps would be to implement this in your MongoDB application and explore more about MongoDB's security features.

Additional resources:
- MongoDB Documentation
- MongoDB Security

5. Practice Exercises

1. Create a user with read role.
2. Authenticate the user you created.

Solutions

1. Create a user with read role:

db.createUser(
  {
    user: "readonlyUser",
    pwd: "readonlyPassword",
    roles: [ "read" ]
  }
)

1. Authenticate the user:

db.auth("readonlyUser", "readonlyPassword")

If successful, this will return 1. Otherwise, it will return 0.

Keep practicing with different users, roles and try to authenticate them.