M3: auth.json credential storage

Adds harness-providers::auth, a persisted auth.json credential store for provider tokens, laying the groundwork for Copilot's device-flow login and token refresh.

Cargo.lock

@@ -723,12 +723,14 @@ dependencies = [
  "async-stream",
  "async-trait",
  "bytes",
+ "dirs",
  "eventsource-stream",
  "futures",
  "harness-core",
  "reqwest",
  "serde",
  "serde_json",
+ "tempfile",
  "thiserror 2.0.18",
  "tokio",
  "tokio-util",

crates/harness-providers/Cargo.toml

@@ -18,9 +18,11 @@ serde = { workspace = true }
 serde_json = { workspace = true }
 thiserror = { workspace = true }
 tracing = { workspace = true }
+dirs = { workspace = true }
 
 [dev-dependencies]
 tokio = { workspace = true, features = ["test-util", "macros"] }
+tempfile = { workspace = true }
 
 [lints]
 workspace = true

crates/harness-providers/src/auth.rs

@@ -0,0 +1,228 @@
+//! Credential storage for providers that authenticate outside the config file.
+//!
+//! A single JSON file (`~/.local/share/ai-harness/auth.json`, mode `0600`) keyed by provider
+//! id. OAuth providers (Copilot) store the token triple and refresh it in place; API-key
+//! providers store the bare key. Config-supplied keys take precedence over this file — this
+//! is only for interactively-obtained credentials.
+
+use std::collections::HashMap;
+use std::io;
+use std::path::{Path, PathBuf};
+
+use serde::{Deserialize, Serialize};
+
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(tag = "type", rename_all = "snake_case")]
+pub enum AuthRecord {
+    /// OAuth credentials. `expires` is a unix-ms timestamp; `0` means the token never expires
+    /// (opencode's direct-Bearer Copilot mode).
+    OAuth {
+        access: String,
+        refresh: String,
+        expires: i64,
+    },
+    Api {
+        key: String,
+    },
+}
+
+impl AuthRecord {
+    /// True when an OAuth token is at or past `expires` (with a safety skew), given `now_ms`.
+    /// API keys and never-expiring OAuth tokens (`expires == 0`) are never considered expired.
+    pub fn is_expired(&self, now_ms: i64, skew_ms: i64) -> bool {
+        match self {
+            AuthRecord::OAuth { expires, .. } if *expires > 0 => now_ms + skew_ms >= *expires,
+            _ => false,
+        }
+    }
+}
+
+/// Read/modify/write access to the auth file. Cheap to construct; every operation reloads so
+/// concurrent writers (a refresh in one provider, a login in another) don't clobber each other.
+#[derive(Debug, Clone)]
+pub struct AuthStorage {
+    path: PathBuf,
+}
+
+impl AuthStorage {
+    pub fn new(path: PathBuf) -> Self {
+        Self { path }
+    }
+
+    /// `~/.local/share/ai-harness/auth.json` (falling back to the temp dir if there is no
+    /// data directory).
+    pub fn default_path() -> PathBuf {
+        dirs::data_dir()
+            .unwrap_or_else(std::env::temp_dir)
+            .join("ai-harness")
+            .join("auth.json")
+    }
+
+    pub fn with_default_path() -> Self {
+        Self::new(Self::default_path())
+    }
+
+    /// Loads all records. A missing file yields an empty map; a corrupt file is an error.
+    pub fn load(&self) -> io::Result<HashMap<String, AuthRecord>> {
+        match std::fs::read(&self.path) {
+            Ok(bytes) => serde_json::from_slice(&bytes)
+                .map_err(|e| io::Error::new(io::ErrorKind::InvalidData, e)),
+            Err(e) if e.kind() == io::ErrorKind::NotFound => Ok(HashMap::new()),
+            Err(e) => Err(e),
+        }
+    }
+
+    pub fn get(&self, provider: &str) -> io::Result<Option<AuthRecord>> {
+        Ok(self.load()?.remove(provider))
+    }
+
+    pub fn set(&self, provider: &str, record: AuthRecord) -> io::Result<()> {
+        let mut records = self.load()?;
+        records.insert(provider.to_string(), record);
+        self.write(&records)
+    }
+
+    pub fn remove(&self, provider: &str) -> io::Result<()> {
+        let mut records = self.load()?;
+        if records.remove(provider).is_some() {
+            self.write(&records)?;
+        }
+        Ok(())
+    }
+
+    /// Serializes `records` and writes them with `0600` permissions via a temp-file rename so
+    /// a partial write can never leave a truncated auth file behind.
+    fn write(&self, records: &HashMap<String, AuthRecord>) -> io::Result<()> {
+        if let Some(parent) = self.path.parent() {
+            std::fs::create_dir_all(parent)?;
+        }
+        let json = serde_json::to_vec_pretty(records)
+            .map_err(|e| io::Error::new(io::ErrorKind::InvalidData, e))?;
+
+        let tmp = self.path.with_extension("json.tmp");
+        std::fs::write(&tmp, &json)?;
+        set_owner_only(&tmp)?;
+        std::fs::rename(&tmp, &self.path)?;
+        Ok(())
+    }
+}
+
+#[cfg(unix)]
+fn set_owner_only(path: &Path) -> io::Result<()> {
+    use std::os::unix::fs::PermissionsExt;
+    std::fs::set_permissions(path, std::fs::Permissions::from_mode(0o600))
+}
+
+#[cfg(not(unix))]
+fn set_owner_only(_path: &Path) -> io::Result<()> {
+    Ok(())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn storage() -> (tempfile::TempDir, AuthStorage) {
+        let dir = tempfile::tempdir().unwrap();
+        let path = dir.path().join("nested").join("auth.json");
+        (dir, AuthStorage::new(path))
+    }
+
+    #[test]
+    fn missing_file_loads_empty() {
+        let (_dir, store) = storage();
+        assert!(store.load().unwrap().is_empty());
+        assert_eq!(store.get("anthropic").unwrap(), None);
+    }
+
+    #[test]
+    fn set_get_roundtrip_and_overwrite() {
+        let (_dir, store) = storage();
+        store
+            .set("anthropic", AuthRecord::Api { key: "k1".into() })
+            .unwrap();
+        assert_eq!(
+            store.get("anthropic").unwrap(),
+            Some(AuthRecord::Api { key: "k1".into() })
+        );
+
+        store
+            .set("anthropic", AuthRecord::Api { key: "k2".into() })
+            .unwrap();
+        assert_eq!(
+            store.get("anthropic").unwrap(),
+            Some(AuthRecord::Api { key: "k2".into() })
+        );
+    }
+
+    #[test]
+    fn multiple_providers_coexist() {
+        let (_dir, store) = storage();
+        store
+            .set("openai", AuthRecord::Api { key: "sk".into() })
+            .unwrap();
+        store
+            .set(
+                "github-copilot",
+                AuthRecord::OAuth {
+                    access: "a".into(),
+                    refresh: "r".into(),
+                    expires: 0,
+                },
+            )
+            .unwrap();
+        let all = store.load().unwrap();
+        assert_eq!(all.len(), 2);
+        assert!(all.contains_key("openai"));
+        assert!(all.contains_key("github-copilot"));
+    }
+
+    #[test]
+    fn remove_deletes_only_named_provider() {
+        let (_dir, store) = storage();
+        store
+            .set("openai", AuthRecord::Api { key: "sk".into() })
+            .unwrap();
+        store
+            .set("anthropic", AuthRecord::Api { key: "an".into() })
+            .unwrap();
+        store.remove("openai").unwrap();
+        assert_eq!(store.get("openai").unwrap(), None);
+        assert!(store.get("anthropic").unwrap().is_some());
+        // Removing an absent provider is a no-op, not an error.
+        store.remove("openai").unwrap();
+    }
+
+    #[test]
+    fn oauth_expiry_respects_skew_and_never_expires() {
+        let never = AuthRecord::OAuth {
+            access: "a".into(),
+            refresh: "r".into(),
+            expires: 0,
+        };
+        assert!(!never.is_expired(i64::MAX, 0));
+
+        let expiring = AuthRecord::OAuth {
+            access: "a".into(),
+            refresh: "r".into(),
+            expires: 1_000,
+        };
+        assert!(!expiring.is_expired(800, 120));
+        assert!(expiring.is_expired(880, 120)); // within skew window
+        assert!(expiring.is_expired(1_000, 0));
+
+        assert!(!AuthRecord::Api { key: "k".into() }.is_expired(i64::MAX, 0));
+    }
+
+    #[cfg(unix)]
+    #[test]
+    fn file_is_written_owner_only() {
+        use std::os::unix::fs::PermissionsExt;
+        let (_dir, store) = storage();
+        store
+            .set("openai", AuthRecord::Api { key: "sk".into() })
+            .unwrap();
+        let mode = std::fs::metadata(&store.path).unwrap().permissions().mode();
+        assert_eq!(mode & 0o777, 0o600);
+    }
+}

crates/harness-providers/src/lib.rs

@@ -1,8 +1,10 @@
 pub mod anthropic;
+pub mod auth;
 pub mod codec;
 pub mod openai;
 pub mod registry;
 
 pub use anthropic::AnthropicProvider;
+pub use auth::{AuthRecord, AuthStorage};
 pub use openai::OpenAiProvider;
 pub use registry::ProviderRegistry;