I have a scenario where one of our vendors needs to acess one of our SharePoint sites to work on some data. I have creating an AD account for him on our internal domain, but the problem is with accessing this site through the internet is it's prompting for his credentials over 10 times before allowing him to log in. I've already tried all the IE tricks to minimize this but I can't get it to work.
Internally I have a GPO that forces an IE setting to use local credentials to sign in so there isn't any prompts since they're already signed into our AD. My initial thought is to maybe create a trust between our AD and our vendors AD and use his local AD's user account to grant access, then have him set his IE settings to the same as my users.
Before I do that however, i'd like to know if this is the best way to achieve this and if anyone know of any resources that go through the process of achieving SSO in SharePoint 2013?