Is it possible to authenticate to third-party service in G-Suite (Gmail) Add-ons, but without oAuth. The service I want to authenticate works on REST API and has no oAuth support.
The best for me would be to open a new window (as with oAuth), login there and return token to the Gmail add-on frame. If that won't be possible, I'd go with giving a username and password in dedicated Card in add-on, but I'm not sure it that solution will pass Google verification when publishing in Marketplace.
I'll be grateful for all the suggestions.