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
/**
     * Returns the authentication version.
     * Nodes can only interpret authentications from current or older versions as the node's.
     *
     * Authentication is serialized and travels across the cluster nodes as the sub-requests are handled,
     * and can also be cached by long-running jobs that continue to act on behalf of the user, beyond
     * the lifetime of the original request.
     */
    public Version getVersion() {
        return version;
    }
    public AuthenticationType getAuthenticationType() {
        return type;
    }
    public Map<String, Object> getMetadata() {
        return metadata;
    }
    /**
     * Returns a new {@code Authentication}, like this one, but which is compatible with older version nodes.
     * This is commonly employed when the {@code Authentication} is serialized across cluster nodes with mixed versions.
     */
    public Authentication maybeRewriteForOlderVersion(Version olderVersion) {
        
        
        Authentication newAuthentication = new Authentication(
            getUser(),
            maybeRewriteRealmRef(olderVersion, getAuthenticatedBy()),
            maybeRewriteRealmRef(olderVersion, getLookedUpBy()),
            olderVersion,
            getAuthenticationType(),