I was able to test github1s for private repos after generating a personal access token, and pasting it into the Set OAuth Token screen (via little github1s icon in the sidebar).
After this was correctly configured, the "Status" indicator on the welcome page turned green and now says "Authorized" (instead of the yellow "Unauthorized" that I initially saw)
After this was correctly configured, the "Status" indicator on the welcome page turned green and now says "Authorized" (instead of the yellow "Unauthorized" that I initially saw)