xDebug integration with CodeIgniter involves manual configuration in the php.ini file. Developers need to enable xDebug, set breakpoints, and configure their IDE for a seamless debugging experience. Composer can also streamline the process.

Mocking in CodeIgniter's unit testing allows developers to isolate the code from external dependencies. Mock objects simulate the behavior of real objects, enabling thorough testing of specific code units without relying on external systems or services. This enhances the reliability and efficiency of unit tests.

DKIM and SPF are essential in email integration. DKIM provides a digital signature to verify the sender's identity, and SPF specifies authorized mail servers. Together, they enhance email security and reduce the risk of email spoofing.

CodeIgniter handles RESTful API authentication through OAuth 2.0, which is a widely used protocol for securing API access. OAuth 2.0 provides a standardized way for applications to authenticate and authorize users without exposing their credentials. This enhances the security of RESTful API interactions in CodeIgniter.

OAuth, or Open Authorization, is a standard protocol for secure and delegated access. It is crucial in social media integration as it allows third-party applications to access user data without exposing login credentials. Understanding OAuth enhances the security and user experience of social media logins in CodeIgniter.

If 'auto-connect' is set to false, the $this->db->initialize() function is used in CodeIgniter to manually connect to the database.

In CodeIgniter, Models can be utilized to implement data validation rules by incorporating validation logic within Model methods. The $this->form_validation library is typically used in Controllers for form validation, but within Models, developers have the flexibility to define custom validation rules and logic tailored to the data layer. This approach helps maintain separation of concerns and ensures that data validation is an integral part of the overall application architecture.

The Unit Testing Library is commonly used in CodeIgniter for unit testing. It provides functions to perform various types of tests, such as checking if two values are equal or validating the existence of a specific item. This library facilitates the creation and execution of unit tests in a CodeIgniter application.

Database Migrations in CodeIgniter play a crucial role in version controlling the database schema. This is particularly beneficial in continuous integration environments, where changes to the database can be tracked, applied, and rolled back systematically, ensuring a consistent and reliable database structure across different environments.

Views in CodeIgniter often use template engines to display data from Models. A template engine separates the presentation logic from the application logic, enhancing maintainability.