The `user_ldap_dn` is optional and is only sent when the user is logged in
through LDAP.
`identities` will contain the details of all the identities associated with the user. This will be an empty array if there are no identities associated with the user.
When the external authorization service responds with a status code 200, the
user is granted access. When the external service responds with a status code
401 or 403, the user is denied access. In any case, the request is cached for 6 hours.