Feature Request: store credentials more securely

[igorbernstein]

Hi,

First I'd like to thank you for this excellent application. Thanks for all of the time you've spent developing it.

I was wondering if it would be possible to use something like keytar to store credentials for saved connections? It seems like they are currently stored in plaintext. For OS X I found them here: ~/Library/Containers/de.t7n.apps.mqtt-explorer/Data/Library/Application Support/MQTT-Explorer/settings.json