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
convertRoleDescriptorsBytesToMap((BytesReference) metadata.get(AuthenticationField.API_KEY_ROLE_DESCRIPTORS_KEY))
                );
                metadata.put(
                    AuthenticationField.API_KEY_LIMITED_ROLE_DESCRIPTORS_KEY,
                    convertRoleDescriptorsBytesToMap(
                        (BytesReference) metadata.get(AuthenticationField.API_KEY_LIMITED_ROLE_DESCRIPTORS_KEY)
                    )
                );
            } else if (authentication.getVersion().before(VERSION_API_KEY_ROLES_AS_BYTES)
                && streamVersion.onOrAfter(VERSION_API_KEY_ROLES_AS_BYTES)) {
                    metadata = new HashMap<>(metadata);
                    metadata.put(
                        AuthenticationField.API_KEY_ROLE_DESCRIPTORS_KEY,
                        convertRoleDescriptorsMapToBytes(
                            (Map<String, Object>) metadata.get(AuthenticationField.API_KEY_ROLE_DESCRIPTORS_KEY)
                        )
                    );
                    metadata.put(
                        AuthenticationField.API_KEY_LIMITED_ROLE_DESCRIPTORS_KEY,
                        convertRoleDescriptorsMapToBytes(
                            (Map<String, Object>) metadata.get(AuthenticationField.API_KEY_LIMITED_ROLE_DESCRIPTORS_KEY)
                        )
                    );
                }
        }
        return metadata;
    }
    private static Map<String, Object> convertRoleDescriptorsBytesToMap(BytesReference roleDescriptorsBytes) {
        return XContentHelper.convertToMap(roleDescriptorsBytes, false, XContentType.JSON).v2();
    }