Improve the README

README.md

@@ -1,2 +1,115 @@
-# lldap
-Light LDAP implementation
+# lldap - Light LDAP implementation for authentication
+
+This project is an lightweight authentication server that provides an
+opinionated, simplified LDAP interface for authentication: clients that can
+only speak LDAP protocol can talk to it and use it as an authentication server.
+
+The goal is _not_ to provide a full LDAP server; if you're interested in that,
+check out OpenLDAP. This server is made to be:
+* simple to setup (no messing around with `slapd`)
+* simple to manage (friendly web UI)
+* opinionated with basic defaults so you don't have to understand the
+  subtleties of LDAP.
+
+It mostly targets self-hosting servers, with open-source components like
+Nextcloud, Airsonic and so on that only support LDAP as a source of external
+authentication.
+
+## Architecture
+
+The server is entirely written in Rust, using [actix](https://actix.rs) and
+[yew](https://yew.rs) for the frontend.
+
+Backend:
+* Listens on a port for LDAP protocol.
+  * Only a small, read-only subset of the LDAP protocol is supported.
+* Listens on another port for HTTP traffic.
+  * The authentication API, based on JWTs, is under "/auth".
+  * The user management API is under "/api" (POST requests only).
+  * The static frontend files are served by this port too.
+
+Note that secure protocols (LDAPS, HTTPS) are currently not supported. This can
+be worked around by using a reverse proxy in front of the server (for the HTTP
+API) that wraps/unwraps the HTTPS messages, or only open the service to
+localhost or other trusted docker containers (for the LDAP API).
+
+Frontend:
+* User management UI.
+* Written in Rust compiled to WASM as an SPA with the Yew library.
+* Based on components, with a React-like organization.
+
+Data storage:
+* The data (users, groups, memberships, active JWTs, ...) is stored in SQL.
+* Currently only SQLite is supported (see
+  https://github.com/launchbadge/sqlx/issues/1225 for what blocks us from
+  supporting more SQL backends).
+
+### Code organization
+
+* `model/`: Contains the shared data, the interface between front and back-end.
+  The data is transferred by being serialized to JSON, for compatibility with
+  other HTTP-based clients.
+* `app/`: The frontend.
+* `src/`: The backend.
+  * `domain/`: Domain-specific logic: users, groups, checking passwords...
+  * `infra/`: API, both HTTP and LDAP
+
+## Authentication
+
+### Passwords
+
+Passwords are hashed using Argon2, the state of the art in terms of password
+storage. They are hashed using a secret provided in the configuration (which
+can be given as environment variable or command line argument as well): this
+should be kept secret and shouldn't change (it would invalidate all passwords).
+
+TODO: Add client-side password hashing.
+
+### JWTs and refresh tokens
+
+When logging in for the first time, users are provided with a refresh token
+that gets stored in an HTTP-only cookie, valid for 30 days. They can use this
+token to get a JWT to get access to various servers: the JWT lists the groups
+the user belongs to. To simplify the setup, there is a single JWT secret that
+should be shared between the authentication server and the application servers;
+and users don't get a different token per application server
+(this could be implemented, we just didn't have any use case yet).
+
+JWTs are only valid for one day: when they expire, a new JWT can be obtained
+from the authentication server using the refresh token. If the user stays
+logged in, they would only have to type their password once a month.
+
+#### Logout
+
+In order to handle logout correctly, we rely on a blacklist of JWTs. When a
+user logs out, their refresh token is removed from the backend, and all of
+their currently valid JWTs are added to a blacklist. Incoming requests are
+checked against this blacklist (in-memory, faster than calling the database).
+Applications that want to use these JWTs should subscribe to be notified of
+blacklisted JWTs (TODO: implement the PubSub service and API).
+
+## Contributions
+
+Contributions are welcome! Just fork and open a PR. Or just file a bug.
+
+We don't have a code of conduct, just be respectful and remember that it's just
+normal people doing this for free on their free time.
+
+Make sure that you run `cargo fmt` in each crate that you modified (top-level,
+`app/` and `model/`) before creating the PR.
+
+### Setup
+
+To bring up the server, you'll need to compile the frontend. In addition to
+cargo, you'll need:
+
+* WASM-pack: `cargo install wasm-pack`
+* rollup.js: `npm install rollup`
+
+Then you can build the frontend files with `./app/build.sh` (you'll need to run
+this after every front-end change to update the WASM package served).
+
+To bring up the server, just run `cargo run`. The default config is in
+`src/infra/configuration.rs`, but you can override it by creating an
+`lldap_config.toml`, setting environment variables or passing arguments to
+`cargo run`.