feat(daemon): add polkit authorizer with permissive + system modes

daemon/src/polkit.rs

@@ -0,0 +1,80 @@
+use std::collections::HashMap;
+use thiserror::Error;
+use zbus::Connection;
+use zvariant::Value;
+
+#[derive(Debug, Error)]
+pub enum PolkitError {
+    #[error("not authorized: {action}")]
+    NotAuthorized { action: String },
+    #[error(transparent)]
+    Bus(#[from] zbus::Error),
+}
+
+#[allow(dead_code)] // wired up in Task 1.8.
+pub enum Polkit {
+    Permissive,
+    System(Connection),
+}
+
+#[allow(dead_code)] // wired up in Task 1.8.
+impl Polkit {
+    pub fn permissive() -> Self {
+        Self::Permissive
+    }
+
+    pub async fn system(conn: Connection) -> Self {
+        Self::System(conn)
+    }
+
+    /// Check whether `pid` may invoke `action`. Permissive always allows; system mode
+    /// calls org.freedesktop.PolicyKit1.Authority.CheckAuthorization on the bus.
+    pub async fn check(&self, action: &str, pid: u32) -> Result<(), PolkitError> {
+        match self {
+            Self::Permissive => Ok(()),
+            Self::System(conn) => system_check(conn, action, pid).await,
+        }
+    }
+}
+
+async fn system_check(conn: &Connection, action: &str, pid: u32) -> Result<(), PolkitError> {
+    // Subject = ("unix-process", { "pid": u32, "start-time": u64 }).
+    // start-time 0 is accepted by polkit; it will look up /proc itself.
+    let mut subject_details: HashMap<&str, Value<'_>> = HashMap::new();
+    subject_details.insert("pid", Value::U32(pid));
+    subject_details.insert("start-time", Value::U64(0));
+
+    let subject = ("unix-process", subject_details);
+    let details: HashMap<&str, &str> = HashMap::new();
+    let flags: u32 = 0; // No interaction; we don't block on auth prompt here.
+    let cancellation_id = "";
+
+    let proxy = zbus::Proxy::new(
+        conn,
+        "org.freedesktop.PolicyKit1",
+        "/org/freedesktop/PolicyKit1/Authority",
+        "org.freedesktop.PolicyKit1.Authority",
+    )
+    .await?;
+
+    let (is_authorized, _is_challenge, _details): (bool, bool, HashMap<String, String>) = proxy
+        .call("CheckAuthorization", &(subject, action, details, flags, cancellation_id))
+        .await?;
+
+    if is_authorized {
+        Ok(())
+    } else {
+        Err(PolkitError::NotAuthorized { action: action.to_string() })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[tokio::test]
+    async fn permissive_always_allows() {
+        let p = Polkit::permissive();
+        p.check("io.dangerousthings.AuthForge.set-policy", 1234).await.unwrap();
+    }
+}