add to slack vs sign in with slack

Question

I have added the 'Add to Slack' button to my web project and it works fine like exchanging the code for an access token and redirecting to a URL of my choice. Now, I am a little bit confused between the 'Sign in with Slack' button. I know that it is used to log individual members in. So does it ask for their organization email and password and log them in or is it for logging in existing slack users? Also, as soon as I click on the sign in with slack button it takes me to a page where it asks me to authorise and leads me to the redirect uri I set for the Add to Slack button.

I see that they both have the same auth flow as mentioned on the slack API documentation except the scope for 'Sign in with Slack' is users.identity.

I am sorry if my question doesn't make much sense as I am pretty new to Slack. Would really appreciate if someone could help me clear some of these doubts about the two buttons

Answer 1

The gist of it is as follows:

Add to Slack

This button is for adding a new Slack app to a Slack team / workspace. You would only run this once for your app and team.

Sign-in with Slack

Is for authenticating existing Slack users to your non-Slack application, e.g. a website. A user will use it every time to sign-in to your website and your website can use it to verify that the user is who he says he is. It works similar to other SSO services, like Google or Facebook sign on, where e.g. .you can use your existing Google account to sign in to a new website.