I have a database with LDAP login enabled. It works fine when logging in through the PIA or when logging into app-designer through the application server.
I need to make app-designer allow me to login with 2-tier mode using LDAP authentication. Is this possible without customization?
I do not think this is possible. 2-tier logs directly into the database and more importantly, does not run the signon peoplecode that does call-outs for LDAP authentication. In fact, 2-tier is really just a Win32 app that runs no peoplecode - it isn't a peoplesoft "application." There is a user callout dll delivered with peoplesoft, and some scant documents on what you have to do to use it - but again, likely not going to meet your need. You may need to use the ldap synch online app engine job to pull in your ldap users to security tables if you want to use those login identities for 2-tier access.
The only delivered way to use LDAP Authentication for App Designer is to use connection 3-Tier through the app server. Only with the 3-Tier connection will the Signon PeopleCode be executed. With 2-Tier, there is no hook to the LDAP Server.
You could look at using the Grey Sparling Desktop Single Signon, which does integrate with App Designer and uses Windows and NTLM to grab Active Directory authentication. This would give you some degree of LDAP Authentication if you Windows machine authenticates with a domain. But it is an add-on product you would need to purchase.
Otherwise, as Epictetus mentioned, you can use the LDAP Username if you have it synced with your PeopleSoft database and use the local password stored in PSOPRDEFN.