Use OS keyring for credential storage

[patrikbraborec]

Problem

Tokens are currently stored in plain text in ~/.apify/auth.json. This is not ideal from a security perspective, and it also makes authentication harder to discover and use programmatically (e.g. for AI agents).

Proposal

• Move credential storage to the OS keyring (Keychain on macOS, Credential Manager on Windows, Secret Service on Linux).
• Fall back to the existing ~/.apify/auth.json file when the keyring is unavailable (e.g. headless Linux without a Secret Service).
• Make authentication discoverable and easy to use for agents.

Reference

• mcpc implementation

Open questions

• If we implement it, it is breaking change? Or we can keep "both versions", and in 2.0.0 remove the plain text implmenetation.
  • Maybe just logout everyone, and make them to login. Or maybe just write script to migrate it.