Depending on the persona, you might have to present a different login screen depending on the application that has been selected. Since Pega 8.4, you can now use the Application URL alias to login directly to a specific application - see https://community.pega.com/knowledgebase/articles/whats-new-pega-platform/simplify-access-application-url-alias-84 for more details
To deliver a different / branded login screen, you can follow these steps
1/ Point the requestor types to your new unauthenticated access group and application
I recommend to change both the PEGA!BROWSER and the PEGA!APP requestor types to your new access group
2/ Resave the 2 HTML fragments Web-Login and pyDisplayAuthScreenSelector into your unauthenticated ruleset
3/ Create a new circumstanced version of pyDisplayAuthScreenSelector
open the base rule pyDisplayAuthScreenSelector and under ‘SaveAs’, select the option ‘Specialize by circumstance’ and enter the name of the app that this circumstanced rule will apply to
for more details, you can watch this video
for more details on how to customize the login screen, the following articles are recommended: