We would like to revisit the `Authentication` class to make it provide better and easier to use interface to the consumers. 

#79809 enables run-as for all authentication schemes in addition to `realm` which is already supported. This adds more complexity to an `Authentication` object and how it should be used. For an example, building the role associated to an user now has to consider whether the user is the authenticated user or run-as user and the authentication scheme of the authenticated user. The existing `Authentication` class can answer all these question today. But its interface and internals are not aligned for these questions and the usage is error prone. For example, the `Authentication` object itself does not know whether the user has run-as. This information is kept by the `User` object. If the `User` object has an `authenticatedUser`, it's the run-as user. Otherwise it is not. But the information about realms for each `User` is directly kept in `Authentication`. Therefore, for full picture, the caller must check both `User` and `Authentication` realms and understands the nuance of their differenent combinations. 

- [x] Refactor CompositeRolesStore to separate roleDescriptors resolving (#80926)
- [ ] Move effective role descriptor checking from Resolver to CompositeRolesStore
- [x] https://github.com/elastic/elasticsearch/issues/81192
- [ ] Replace Authentication with AuthenticationContext in places other than CompositeRolesStore
x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/security/authc/Authentication.java
return authenticatingSubject.getType() == Subject.Type.API_KEY;
    }
    
    private boolean isAuthenticatedAnonymously() {
        return AuthenticationType.ANONYMOUS.equals(getAuthenticationType());
    }
    private boolean isAuthenticatedInternally() {
        return AuthenticationType.INTERNAL.equals(getAuthenticationType());
    }
    /**
     * Authenticate with a service account and no run-as
     */
    public boolean isServiceAccount() {
        return effectiveSubject.getType() == Subject.Type.SERVICE_ACCOUNT;
    }
    /**
     * Whether the effective user is an API key, this including a simple API key authentication
     * or a token created by the API key.
     */
    public boolean isApiKey() {
        return effectiveSubject.getType() == Subject.Type.API_KEY;
    }
    /**
     * Whether the authentication can run-as another user
     */
    public boolean supportsRunAs(@Nullable AnonymousUser anonymousUser) {
        
        if (isRunAs()) {
            return false;
        }