The "External" flag is missing on the Resource properties.
Administration => Organization and Access => Resources
Click on the Resource
A checkbox called "EXTERNAL" should be displayed, as shown below.
<Please see attached file for image>
LDAP authentication has been enabled but the option "Allow non/LDAP users" is not checked.
CA PPM 15.x
To enable "external authentication" in resources properties, you can try the following steps:
1- login to the NSA/CSA.
2- click on "Application" tab and enable "use LDAP".
3- click on "save" to save the change.
4- next click on "security" tab and enable "allow non-LDAP users" flag.
5- save the change.
6- restart the CA PPM services (APP and BG).
Log back in to PPM and confirm if you can now see the flag "External Authentication" on the Resource Properties page.