The primary responsibility of an OAuth2 Authorization Server in a Spring Boot application is to authenticate users and grant access tokens to authorized clients. It does not store user passwords but rather validates user credentials and authorizes access to protected resources. It also does not manage user profiles and preferences, nor does it control database access; these are typically the tasks of the application's authentication system and database itself.

To optimize the performance of Spring Data JPA when dealing with large datasets, using PagingAndSortingRepository is recommended to read the datasets in chunks. This repository interface extends CrudRepository and provides methods for pagination and sorting, making it suitable for efficiently fetching and processing large datasets by breaking them into manageable chunks.

To customize access-denied behavior, you should implement a custom AccessDeniedHandler, which allows you to define how to handle access-denied situations. You then register this handler with Spring Security to apply it to secured methods.

The spring.profiles.active property in Spring Boot's application properties or YAML file is used to specify the default active Spring profile. Profiles allow you to customize the application's configuration based on the environment (e.g., development, production) or other criteria. By setting this property, you determine which profile is active by default when your Spring Boot application starts. The other options are not the primary purpose of this property.

The TestRestTemplate is a test utility in Spring Boot for making HTTP requests to your application during integration tests. It can be auto-configured and is designed for use in integration testing scenarios.

When encountering security configuration issues during testing, it's crucial to create test-specific security configurations (Option 2) that mimic the production environment. Disabling security (Option 1) or ignoring security issues (Option is not recommended, as it can lead to inaccurate test results. Abandoning testing (Option 4) is not a solution.

The @PreAuthorize annotation is used in Spring Security to enforce security constraints on methods at a fine-grained level. You can specify a SpEL (Spring Expression Language) expression as a condition for method access. If the condition evaluates to true, access is allowed.

The @Transactional annotation in Spring Data JPA is significant because it ensures that if an exception is thrown within the annotated method, the current transaction will be rolled back. This is crucial for maintaining data consistency and integrity. While the other options may have some relevance in JPA, they do not directly represent the primary significance of @Transactional in this context.

In Spring Boot, the @WebMvcTest annotation is used for testing the web layer. It disables full auto-configuration and focuses on relevant web configurations, making it ideal for testing web components like controllers.

The CrudRepository in Spring Data JPA generally provides methods for CRUD (Create, Read, Update, Delete) operations. It's a fundamental repository interface for basic data manipulation tasks. The other mentioned repositories extend CrudRepository and provide additional functionality such as pagination, sorting (JpaRepository), and specification-based querying (JpaSpecificationExecutor).