AuthenticationManager

AuthenticationManager is a class in Spring Security framework that provides central authentication processing for Spring Security. It acts as an entry point to the Spring Security authentication process and determines whether a user is authorized to access a particular resource or not. The AuthenticationManager interface defines two methods: authenticate() and supports(). The authenticate() method takes an Authentication object as input and returns an authenticated Authentication object. The supports() method returns a boolean indicating whether the AuthenticationManager can authenticate the given Authentication object or not.

AuthenticationManager is responsible for:

1. Receiving and processing the authentication request
2. Authenticating the user's credentials
3. Returning an authenticated principal object (or an exception if authentication fails)
4. Managing the authentication process for multiple authentication providers if necessary

The AuthenticationManager interface is implemented by several classes in Spring Security, including ProviderManager and ProviderManagerResolver. The ProviderManager class is the most commonly used implementation of AuthenticationManager, which delegates the authentication process to a list of AuthenticationProvider instances. The ProviderManagerResolver is used to dynamically resolve the appropriate ProviderManager based on the request.