You can set up Weblogic to use an external LDAP (it uses a built-in one by default), but you can't manage it through Weblogic. I use
Apache Directory Studio.
Once you have your LDAP set up, open the Weblogic console and create an Authenticator under Security Realms->myrealm->Providers. You'll need to provide the appropriate contact and mapping information for your configuration. That all depends on how you set up the database and for those details you'll have to rely on the provider's documentation.