# Letro Authentication Service

This repository contains Letro's fork of the
[Matrix Authentication Service (MAS)](https://github.com/element-hq/matrix-authentication-service),
the OIDC-based authentication service for Matrix homeservers,
developed by [Element](https://element.io/) (Element Creations Ltd. /
New Vector Ltd.).

It is published as the corresponding source for the Letro-operated
authentication service, in compliance with the GNU Affero General
Public License, version 3 (AGPLv3) §13.

## Role in the Letro stack

The Letro Authentication Service is the OIDC provider used by the
Letro-operated Matrix homeserver for sign-in, sign-up, account
management and session handling. It is deployed alongside the
homeserver via the unmodified upstream
[Element Server Suite (ESS) Helm chart](https://github.com/element-hq/ess-helm)
and is exposed to end users of the Letro service. Because the
service is reached by users over a network and Letro modifies it,
AGPLv3 §13 applies: every user interacting with the running service
must be offered access to the corresponding source — see
"Corresponding source" below.

## Relationship to upstream

- Upstream project: <https://github.com/element-hq/matrix-authentication-service>
- Upstream baseline used by this fork: see
  [`UPSTREAM_VERSION`](UPSTREAM_VERSION)
- Letro modifications, with dates, serving as the AGPLv3 §5(a)
  modification notice for the work as a whole: see
  [`FORK_DIVERGENCE.md`](FORK_DIVERGENCE.md)

Upstream technical documentation — build instructions, configuration
reference, operations notes — applies unchanged. See the upstream
[README](https://github.com/element-hq/matrix-authentication-service#readme)
and [docs](https://element-hq.github.io/matrix-authentication-service/).

## Status

This repository is the production source for the authentication
service deployed by the Letro-operated homeserver. It is published
primarily to satisfy AGPLv3 §13; it is not a generally supported
open-source project and is not intended for third-party reuse.

## Copyright

```
Copyright (c) 2026 Letro Tech GmbH <legal@letro.com>  -- modifications
```

The upstream copyright lines (Element Creations Ltd., New Vector
Ltd., and the other upstream contributors) are preserved verbatim
in the source files and in [`LICENSE`](LICENSE), as required by
AGPLv3. Letro does not claim authorship of upstream code; the parts
modified by Letro are identified in
[`FORK_DIVERGENCE.md`](FORK_DIVERGENCE.md).

## License

This software is dual-licensed by Element Creations Ltd. ("Element"):

1. for free under the GNU Affero General Public License, version 3
   or (at your option) any later version (AGPLv3); or
2. under a paid Element Commercial License agreement between you and
   Element.

Letro distributes this fork under option (1), AGPLv3. The full
licence texts are in [`LICENSE`](LICENSE) and
[`LICENSE-COMMERCIAL`](LICENSE-COMMERCIAL). Letro's own modifications
are likewise licensed under AGPLv3.

## Third-party components

The authentication service depends on third-party libraries under
their own licences. A consolidated attribution list, generated from
the Cargo dependency graph, is published at
[`THIRD_PARTY_LICENSES.md`](THIRD_PARTY_LICENSES.md).

## Trademarks

"Matrix" is a trademark of The Matrix.org Foundation C.I.C.

"Element", "Matrix Authentication Service" and "MAS" are trademarks
of Element Creations Ltd. / New Vector Ltd.

Letro is **not** affiliated with, endorsed by, or sponsored by The
Matrix.org Foundation or Element. References to the foregoing names
in this repository's source, documentation, history and
configuration are made solely to identify the upstream protocol and
the upstream project from which Letro is derived, as permitted by
nominative fair use.

## Contact

Legal / licensing questions: <legal@letro.com>
Operating entity / imprint: see <https://www.letro.com/imprint>