macOS Keychain-backed credentials provider (feat/credentials-keychain)

[23n0n]

feat(credentials): macOS Keychain-backed credentials provider

Problem Statement

The current file-based credentials provider (dsh-credentials-local) stores secrets in $DSH_HOME/.credentials.yaml with 0600 permissions. While this prevents access by other OS users, it fails to protect against the harness’s own agent processes. Since these agents run under the same user context, they can trivially read the plaintext file. As the documentation notes, the file provider offers "discretion, not a boundary." This leaves sensitive credentials exposed to any process executing within the same user space, undermining the security model for multi-tenant or privileged agent environments.

Context

The credentials-local README explicitly identifies this limitation, stating that an "OS-keychain provider" is the "deferred answer" and should "belong beside this provider as a sibling package." We have now implemented that deferred answer.

Proposed Solution

We introduce a working sibling package: @deepseek-ai/dsh-credentials-keychain. This provider leverages the macOS Login Keychain to store credentials as generic-password items, ensuring secrets are never written to disk in plaintext.

Key Design Features

• Security Mechanism: Uses the /usr/bin/security CLI. Secrets are fed through stdin (never argv) and protected by Keychain Access Control Lists (ACLs).
• Full Seam Implementation: Implements the complete CredentialProvider interface, including:
  • References: resolve, describe, set, unset.
  • Records: readRecord, describeRecord, listRecords, modifyRecord, deleteRecord.
• Mapping Logic:
  • A reference maps to a generic-password item where the account field equals the reference name.
  • A record maps to an item with account record:<scope>/<id>, storing a JSON payload.
• Configuration: Supports service (default: dsh-credentials) and optional custom keychain paths.
• Resolution Logic: Implements environment-wins-over-Keychain resolution with event fan-out.

Scope and Constraints

This provider is macOS-only, relying on native Keychain APIs. It is designed to sit alongside dsh-credentials-local as a drop-in replacement for users requiring stronger isolation from same-user processes.

Please review the implementation and integration details in the next comment

[23n0n]

Fork with the package is ready — the upstream repo blocks API PR creation, so the change lives on a fork:

• Fork repo: https://github.com/23n0n/deepseek-harness
• Package: packages/credentials/credentials-keychain
• Branch: feat/credentials-keychain
• Open the PR from the fork (base master): https://github.com/23n0n/deepseek-harness/pull/new/feat/credentials-keychain

Status: pnpm build:lib:host clean, 4/4 unit tests pass, pre-commit lint + pre-push typecheck green. macOS-only (login Keychain via /usr/bin/security, values through stdin never argv). Sibling to dsh-credentials-local, implementing the full CredentialProvider seam (references + records) with environment-wins resolution.

[WeZZard]

I just think this is a great feature.