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
private final String nodeName;
        private final String name;
        private final String type;
        private final @Nullable RealmDomain domain;
        public RealmRef(String name, String type, String nodeName) {
            this(name, type, nodeName, null);
        }
        public RealmRef(String name, String type, String nodeName, @Nullable RealmDomain domain) {
            this.nodeName = Objects.requireNonNull(nodeName, "node name cannot be null");
            this.name = Objects.requireNonNull(name, "realm name cannot be null");
            this.type = Objects.requireNonNull(type, "realm type cannot be null");
            this.domain = domain;
        }
        public RealmRef(StreamInput in) throws IOException {
            this.nodeName = in.readString();
            this.name = in.readString();
            this.type = in.readString();
            if (in.getVersion().onOrAfter(VERSION_REALM_DOMAINS)) {
                this.domain = in.readOptionalWriteable(RealmDomain::readFrom);
            } else {
                this.domain = null;
            }