fix: unbreak machine account login on macOS#147
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The macOS Keychain has a per-item size limit (~4 KB). Machine account sessions exceeded it because StoredCredentials embedded a full PEM-encoded RSA private key alongside the access token, pushing the blob to ~5 KB. Logins would authenticate successfully but then fail with "data passed to Set was too big" when writing to the keyring, leaving no usable session behind. Store the PEM private key in a 0600 file under the user config directory and keep only a PrivateKeyPath pointer in the keyring blob. The access token continues to live in the OS keyring. Token refresh reads the PEM from disk on demand; logout removes the file alongside the keyring entry. Existing Linux sessions (where the PEM fit in the keyring inline) continue to work without migration: if PrivateKey is still set in the blob, it is used as-is; otherwise PrivateKeyPath is consulted. Fixes #146 Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
- Enforce 0700 perms on existing machine-accounts directory, not just on first creation - Use os.CreateTemp for atomic writes so concurrent logins for the same machine account cannot race on the same .tmp filename - Remove the on-disk PEM if the keyring write fails during login, so failed logins don't leave crypto material behind - Also remove the PEM from disk in the logout "user not found but stray state" branch — this is the exact cleanup path users will hit after a failed #146 login - Use WrapUserErrorWithHint for the token refresh error paths to match the surrounding style; acknowledge in the hint that the original credentials file may no longer be available Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
kevwilliams
approved these changes
Apr 10, 2026
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Summary
On macOS, logging in with a machine account credentials file authenticates successfully but then fails with
error: failed to store credentials in keyring ... data passed to Set was too big, leaving no usable session behind. Machine account logins are effectively broken on macOS today.The cause is a size limit on macOS Keychain items (~4 KB): the machine account session stored a full PEM-encoded RSA private key alongside the access token, pushing the blob over the limit. Interactive (browser) login doesn't hit this because it has no private key to store.
What changed for users
~/Library/Application Support/datumctl/machine-accounts/on macOS,~/.config/datumctl/machine-accounts/on Linux,%AppData%\datumctl\machine-accounts\on Windows). The access token continues to live in the OS keyring/keychain.Fixes #146
Test plan
datumctl auth login --credentials ./my-key.jsonon macOS — completes without the keyring size error and leaves a working sessiondatumctlcommands use the machine-account session (token refresh works after the initial token expires)datumctl auth logout <machine-account>removes the session and cleans up the on-disk key file🤖 Generated with Claude Code