This article explains how to create a new Linkedin custom App and obtain the right permissions to use it.
STEP 1
Go to https://www.linkedin.com/secure/developer and click on "Create Application".

STEP 2
Fill in the App information section with the required data:

In the Products section leave the default, and accept the terms in Legal terms, then click on Create app button

STEP 3
Access to the Auth tab and set the "OAuth 2.0 Redirect URLs" field with the following information, then update
https://YOURDOMAIN/index.php?action=oauth_linkedin_callback
CAUTION
Replace YOURDOMAIN with your current domain.

After upgrading, permissions will be visible in the appropriate section:

STEP 4
In the Products tab > Added products, verify you have "Share on Linkedin" and "Sign In with Linkedin" products

STEP 5
Copy the
Client ID and the
Client Secret from
Auth tab and set them in White Label Splash Editor.
Related Article:
How to configure the Tanaza Splash Page to work with your custom app