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Letro Authentication Service
This repository contains Letro's fork of the Matrix Authentication Service (MAS), the OIDC-based authentication service for Matrix homeservers, developed by Element (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 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 - Letro modifications, with dates, serving as the AGPLv3 §5(a)
modification notice for the work as a whole: see
FORK_DIVERGENCE.md
Upstream technical documentation — build instructions, configuration reference, operations notes — applies unchanged. See the upstream README and docs.
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, as required by
AGPLv3. Letro does not claim authorship of upstream code; the parts
modified by Letro are identified in
FORK_DIVERGENCE.md.
License
This software is dual-licensed by Element Creations Ltd. ("Element"):
- for free under the GNU Affero General Public License, version 3 or (at your option) any later version (AGPLv3); or
- 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 and
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.
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