users: a user manages its own keys

Only a user who may manage users could change a user's keys: a user
couldn't add a new laptop's key, or remove a lost one.

A user now manages its own keys, whatever else it may do:

* GET /auth/keys: its keys, its entry, and the envelope holding it
  under a strict policy (`signed`), to sign against.
* PUT /auth/keys/{id} with an authorized_keys line, DELETE
  /auth/keys/{id}: one change, as the user. The rules take a write of
  _continuum/users/<name>/keys/… from the user it names.
* Under a strict policy, the user signs its entry with only its keys
  changed, with a key it holds already (envelope::check takes that from
  the user itself), PUT to its own entry even without write on the
  registry; continuum-signed key-add and key-remove do so.

3 files changed, 118 insertions, 1 deletions

diff --git a/src/api/mod.rs b/src/api/mod.rs
index 0e7fc21..43d3c20 100644
--- a/src/api/mod.rs
+++ b/src/api/mod.rs
@@ -74,6 +74,11 @@ pub(crate) fn router(state: AppState, auth_state: AuthState, debug_api: bool) ->
         )
         .route("/auth/logout", axum::routing::post(login::logout))
         .route("/auth/whoami", get(login::whoami))
+        .route("/auth/keys", get(users::own_keys))
+        .route(
+            "/auth/keys/{id}",
+            axum::routing::put(users::put_own_key).delete(users::delete_own_key),
+        )
         .route("/admin/users", get(users::list).post(users::add_several))
         .route("/admin/users/{name}/tokens", delete(users::revoke_tokens))
         .route(
diff --git a/src/api/store.rs b/src/api/store.rs
index 81d0046..16dd966 100644
--- a/src/api/store.rs
+++ b/src/api/store.rs
@@ -464,7 +464,16 @@ pub(crate) async fn put_store_entry(
         return Err(StatusCode::SERVICE_UNAVAILABLE.into());
     }
 
-    let path = parse_write_path(&state, &user, &access, &key, "PUT")?;
+    // A user's own entry, signed by it: its keys are its own to change, whatever else it
+    // may do (`envelope::check` takes nothing else changed).
+    let own_entry = media_type(&headers) == SIGNED
+        && parse_key_path(&key)
+            .is_ok_and(|path| path == crate::access::registry::user_path(&user.0));
+    let path = if own_entry {
+        crate::access::registry::user_path(&user.0)
+    } else {
+        parse_write_path(&state, &user, &access, &key, "PUT")?
+    };
     let sign = Sign::Write {
         path: path.clone(),
         asked: query.signed,
diff --git a/src/api/users.rs b/src/api/users.rs
index 8972566..122fc4b 100644
--- a/src/api/users.rs
+++ b/src/api/users.rs
@@ -18,6 +18,15 @@
 //!   one exists. How a swarm without a registry gets one, the caller among those who
 //!   may manage users.
 //!
+//! A user manages its own keys (`keys`, `authorized_keys` lines), whatever it may do
+//! otherwise:
+//!
+//! * `GET /auth/keys`: the caller's keys, its entry, and the envelope holding it under a
+//!   strict policy (`signed`), to sign the next one against.
+//! * `PUT /auth/keys/{id}`: one added or replaced (the line as the body);
+//!   `DELETE /auth/keys/{id}` removes one. Under a strict policy `409`: the user signs
+//!   its entry with the keys changed, nothing else (`continuum-signed key-add`).
+//!
 //! Looking needs `read` on `_continuum/users`, changing `write` on it (in a swarm
 //! without a registry, being in `--protocol-writers`). Every change is one change to
 //! the document, logged, named by who made it, and refused (`409`) where it would lock
@@ -129,6 +138,100 @@ fn shown(doc: &impl crate::document::ReadDoc, name: &str) -> Option<JsonValue> {
     Some(entry)
 }
 
+/// `GET /auth/keys`.
+pub(crate) async fn own_keys(
+    State(state): State<AppState>,
+    Extension(user): Extension<AuthenticatedUser>,
+) -> Result<Json<JsonValue>, ApiError> {
+    let replica = state.doc.read().await;
+    let path = registry::user_path(&user.0);
+    let entry = store::read_plain(&replica.doc, &path)
+        .ok()
+        .flatten()
+        .ok_or_else(|| ApiError(StatusCode::NOT_FOUND, Some("no entry of yours".to_owned())))?;
+    let signed = match store::read_path(&replica.doc, &path) {
+        Ok(Some(JsonValue::String(text))) if text.starts_with("cv1.") => Some(text),
+        _ => None,
+    };
+    Ok(Json(json!({
+        "keys": entry.get("keys").cloned().unwrap_or_else(|| json!({})),
+        "entry": entry,
+        "signed": signed,
+    })))
+}
+
+/// `PUT /auth/keys/{id}`.
+pub(crate) async fn put_own_key(
+    State(state): State<AppState>,
+    Extension(user): Extension<AuthenticatedUser>,
+    Path(id): Path<String>,
+    body: String,
+) -> Result<StatusCode, ApiError> {
+    let key = crate::access::sshsig::PublicKey::parse(body.trim()).map_err(|why| bad(&why))?;
+    own_key(&state, &user.0, id, Some(key.line())).await
+}
+
+/// `DELETE /auth/keys/{id}`.
+pub(crate) async fn delete_own_key(
+    State(state): State<AppState>,
+    Extension(user): Extension<AuthenticatedUser>,
+    Path(id): Path<String>,
+) -> Result<StatusCode, ApiError> {
+    own_key(&state, &user.0, id, None).await
+}
+
+/// `user`'s key `id` set to `line`, or removed: one change, as `user`.
+async fn own_key(
+    state: &AppState,
+    user: &str,
+    id: String,
+    line: Option<String>,
+) -> Result<StatusCode, ApiError> {
+    if !registry::valid_name(&id) {
+        return Err(bad("not a key's name: 1 to 64 of A-Z a-z 0-9 . _ @ -"));
+    }
+    if !state.is_ready().await {
+        return Err(StatusCode::SERVICE_UNAVAILABLE.into());
+    }
+    let entry = registry::user_path(user);
+    let mut path = entry.clone();
+    path.extend(["keys".to_owned(), id.clone()]);
+    let adding = line.is_some();
+    state
+        .mutate_doc_for(Some(user.to_owned()), Sign::Protocol, move |doc| {
+            if crate::access::policy::of(&*doc).strict() {
+                return Err(ApiError(
+                    StatusCode::CONFLICT,
+                    Some(
+                        "users sign their entries (strict policy): sign yours with the keys \
+                         changed (continuum-signed key-add, key-remove)"
+                            .to_owned(),
+                    ),
+                ));
+            }
+            if store::read_path(&*doc, &entry)?.is_none() {
+                return Err(ApiError(
+                    StatusCode::NOT_FOUND,
+                    Some("no entry of yours".to_owned()),
+                ));
+            }
+            match line {
+                Some(line) => store::write_path(doc, &path, &json!(line))?,
+                None => match store::delete_path(doc, &path, false) {
+                    Ok(()) => {}
+                    Err(crate::document::store::StoreError::NotFound) => {
+                        return Err(ApiError(StatusCode::NOT_FOUND, None));
+                    }
+                    Err(error) => return Err(error.into()),
+                },
+            }
+            Ok(())
+        })
+        .await?;
+    info!(user = %user, key = %id, "{}", if adding { "Set own key" } else { "Removed own key" });
+    Ok(StatusCode::NO_CONTENT)
+}
+
 /// `GET /admin/users`.
 pub(crate) async fn list(State(state): State<AppState>) -> Json<JsonValue> {
     let replica = state.doc.read().await;