Securely passing credentials from Installer plug-in to newly installed agent — how to authenticate the caller?

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Created 2d

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I’m using a custom Installer plug-in (InstallerPane) to collect sensitive user input (username/password) during install. After the payload is laid down, I need to send those values to a newly installed agent (LaunchAgent) to persist them.

What I tried

I expose an XPC Mach service from the agent and have the plug-in call it.

On the agent side I validate the XPC client using the audit token → SecCodeCopyGuestWithAttributes → SecCodeCheckValidity.

However, the client process is InstallerRemotePluginService-* (Apple’s view service that hosts all plug-ins), so the signature I see is Apple’s, not mine. I can’t distinguish which plug-in made the call.

Any suggestion on better approach ?

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Answer 1

DTS Engineer OP

Apple

1d

I can’t distinguish which plug-in made the call.

Correct. Installer plug-ins are old school in-process plug-ins, where the code gets loaded by the host process. Apple platforms establish security boundaries at the process level. Those two facts make it impossible to determine the identity of the caller.

I’m not super familiar with installer plug-ins, so I’m gonna ask what might seem like an obvious question: Is your plug-in able to spawn a child process? If so, you could bundle a separate program within your plug-in, have the plug-in spawn it, and then have that process do the XPC.

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