# Architecture

## Online authentication

```text
LogonUI
  -> SGU Credential Provider (SecureString)
      -> HTTPS 1.1 + client certificate
          -> SGU Auth Broker
              -> SGU IIS NTLM endpoint (original password)
              -> minimum SGU profile metadata (same authenticated response)
              -> Active Directory (same original password + optional profile)
          <- domain + canonical username; never a password
      -> Windows credential serialization (original SecureString)
  -> LSA / Kerberos / cached domain logon
```

The broker performs the NTLM exchange and AD update before returning `200 OK`.
It follows only HTTPS redirects whose host appears in `AllowedRedirectHosts`,
which prevents credential forwarding to an unexpected redirect target. HTTP/1.1
is forced because NTLM authentication is connection-bound.

The logical GET is sent directly to the administrative incident overview for
`AD` identities, the student information page for `AL` identities, or the
portal menu for `DO` identities. NTLM may still require its normal
challenge/response round trips on that connection. The broker keeps any
transient portal cookie in an in-memory per-request container; it is never
persisted or returned to the client.

## Offline authentication

```text
Broker timeout, TLS failure, 429, or 5xx
  -> provider preserves the entered username/password
  -> Windows LSA validates against AD or its cached domain verifier
  -> only the last AD password succeeds
```

An explicit `400` or `401` from the broker is different: the provider displays
an error and does not serialize the rejected credential.

## Account synchronization

The broker normalizes the username to uppercase and accepts exactly two letters
plus six digits. It searches `BaseDn` by `sAMAccountName`, creates the user when
absent, moves it to the mapped OU when required, sets `userPrincipalName`, and
passes the submitted password directly to ADSI `SetPassword`.

When the authenticated HTML exposes recognized stable IDs, the broker also
updates the applicable `displayName`, `givenName`, `sn`, `mail`, `title`,
`department`, `employeeType`, `employeeID`, `streetAddress`, `l`, `st`, and
`postalCode` attributes. Administrative and student numbers must match the six
numeric digits of the requested identity before any scraped metadata is
trusted. Student faculty/department is deliberately left unset because the
verified page does not expose it. Missing metadata does not clear existing AD
values and never changes the password outcome.

Human-readable SGU values are decoded with BOM/header/meta detection, strict
UTF-8 validation, and a Windows-1252 fallback for the legacy portal. Names and
titles are normalized with Spanish-aware casing; particles such as `de`, `del`
and `de la` remain lowercase and Unicode accents are preserved. Values that
still contain the Unicode replacement character are not written to AD.

When `RemoteDesktopGroupDn` is configured, the broker also adds each successfully
synchronized SGU user to that dedicated AD security group. The laboratory
Windows client maps the group into its local **Remote Desktop Users** group.
Every synchronized user also receives `Universidad La Salle` in the AD
`company` attribute unless deployment configuration supplies another default.

The generic SGU credential is rendered as a dedicated branded tile instead of
being grouped below the anonymous **Other user** tile. Machine policy assigns
the SGU CLSID as the default provider while retaining the built-in Microsoft
password provider. It enumerates one `CPFT_TILE_IMAGE` and places the
`CPFT_LARGE_TEXT` heading immediately after it with `CPFS_DISPLAY_IN_BOTH`,
matching Microsoft's supported field ordering. LogonUI owns field typography:
on Windows 10 and 11, the account-name title used by **Other user** is shell UI,
not a style that a generic Credential Provider can request. Do not add a second
tile image or a synthetic Windows account to imitate that title.

The managed hierarchy is rooted at `OU=Usuarios-SGU`: `Docentes`, `Alumnos`,
and `Administrativos` are direct child OUs beneath it.

Per-user synchronization is serialized inside the broker to prevent concurrent
create/reset races. Production deployments should run the broker as a gMSA with
delegated create-user, move-user, write-property, enable-account, and reset-password
rights limited to `Usuarios-SGU` and its three managed child OUs. The lab can run it on the domain
controller as LocalSystem.