Handling secrets
### Current Situation

Good morning!

I'm the author of [homebridge-tapo-camera](https://github.com/kopiro/homebridge-tapo-camera) and I'm here to propose / discuss a way to better handle passwords in homebridge.

Currently, the only way to access RTSP streams for the camera is to to provide username + password in the URL, and these values coming from `config.json` itself.

The problem with this approach is since these passwords are stored in a plain `.json` file, any plugin can actually read `/var/lib/homebridge/config.json`, leaving these secretes exposes to possible compromised plugins.


### Proposed Change

Without going directly into solution mode, I'd like to discuss several approaches:

### Using builtin OSes users

Running child bridges as different users, created dynamically on-the-fly for every bridge (`homebridge-child1`), all part of `homebridge` group. The `config.json` file would only be readable by the `homebridge` user and it would inject in memory only the chunk of config related to that child-bridge, making it unable for the child-bridge to directly read the file.

### Keychains

Not really sure about the technlogy to use here, but something similar to what SSH does with the built-in keychain, where it request a private key to the OS and it's authenticated only for certain software. This would remove the password from the file itself, having a better mechanism to retrieve secrets for all plugins.


### Additional Context

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