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
null,
            Version.CURRENT,
            AuthenticationType.API_KEY,
            authResult.getMetadata()
        );
        assert false == authentication.isAssignedToDomain();
        return authentication;
    }
    private static RealmRef maybeRewriteRealmRef(Version streamVersion, RealmRef realmRef) {
        if (realmRef != null && realmRef.getDomain() != null && streamVersion.before(VERSION_REALM_DOMAINS)) {
            
            new RealmRef(realmRef.getName(), realmRef.getType(), realmRef.getNodeName(), null);
        }
        return realmRef;
    }
    @SuppressWarnings("unchecked")
    private static Map<String, Object> maybeRewriteMetadataForApiKeyRoleDescriptors(Version streamVersion, Authentication authentication) {
        Map<String, Object> metadata = authentication.getMetadata();
        
        
        if (authentication.isAuthenticatedAsApiKey()) {
            assert metadata.containsKey(AuthenticationField.API_KEY_ROLE_DESCRIPTORS_KEY)
                : "metadata must contain role descriptor for API key authentication";
            assert metadata.containsKey(AuthenticationField.API_KEY_LIMITED_ROLE_DESCRIPTORS_KEY)
                : "metadata must contain limited role descriptor for API key authentication";
            if (authentication.getVersion().onOrAfter(VERSION_API_KEY_ROLES_AS_BYTES)
                && streamVersion.before(VERSION_API_KEY_ROLES_AS_BYTES)) {
                metadata = new HashMap<>(metadata);
                metadata.put(
                    AuthenticationField.API_KEY_ROLE_DESCRIPTORS_KEY,