1. You should be using RemoteAuth Authentication using the RemoteAuth: Customizing Settings documentation along with EZproxy or just use LDAP Authentication using the LDAP Authentication: Customizing Settings.
2. If you are using Shibboleth and you are Self-hosted, Atlas has documentation on their Configuring ILLiad to Use OpenAthens documentation.
2. Using OpenAthens directly into ILLiad is still in development at ATLAS.