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/Subject.java
}
        return new RoleReferenceIntersection(
            new RoleReference.ApiKeyRoleReference(apiKeyId, roleDescriptorsBytes, RoleReference.ApiKeyRoleType.ASSIGNED),
            limitedByRoleReference
        );
    }
    private static boolean isEmptyRoleDescriptorsBytes(BytesReference roleDescriptorsBytes) {
        return roleDescriptorsBytes == null || (roleDescriptorsBytes.length() == 2 && "{}".equals(roleDescriptorsBytes.utf8ToString()));
    }
    private RoleReferenceIntersection buildRolesReferenceForApiKeyBwc() {
        final String apiKeyId = (String) metadata.get(AuthenticationField.API_KEY_ID_KEY);
        final Map<String, Object> roleDescriptorsMap = getRoleDescriptorMap(API_KEY_ROLE_DESCRIPTORS_KEY);
        final Map<String, Object> limitedByRoleDescriptorsMap = getRoleDescriptorMap(API_KEY_LIMITED_ROLE_DESCRIPTORS_KEY);
        if (roleDescriptorsMap == null && limitedByRoleDescriptorsMap == null) {
            throw new ElasticsearchSecurityException("no role descriptors found for API key");
        } else {
            final RoleReference.BwcApiKeyRoleReference limitedByRoleReference = new RoleReference.BwcApiKeyRoleReference(
                apiKeyId,
                limitedByRoleDescriptorsMap,
                RoleReference.ApiKeyRoleType.LIMITED_BY
            );
            if (roleDescriptorsMap == null || roleDescriptorsMap.isEmpty()) {
                return new RoleReferenceIntersection(limitedByRoleReference);
            } else {
                return new RoleReferenceIntersection(
                    new RoleReference.BwcApiKeyRoleReference(apiKeyId, roleDescriptorsMap, RoleReference.ApiKeyRoleType.ASSIGNED),
                    limitedByRoleReference
                );
            }
        }