What does this do? Will this provide a custom OAuth UI?

We support two way for generating auth URL to authenticate users

connectedAccounts.initiate

and

connectedAccounts.link

The first one allows you to build your own UI on top of Composio's fields and just send the values to initate a connection. For OAuth apps, when you initiate a connection we return a URL to redirect the user. With this option enabled, we will return the link which is our hosted auth experience, similar to what you get with

connectedAccounts.link

which handles all the auth fields required so you don't have to render it. We added this option because with generating OAuth links with initiate there is a security concern around account take over where anyone can authenticate users on your behalf into your account. With this link experience the issue gets solved.