How can I customize the RH-SSO login page's logic?

Issue

• Currently we are on PicketLink with our IDPhas custom servlet to login ( via HTTP POST) to IBM WebSphere and SAP to get cookies and set cookies back to user's browser.
• For more info we get cookie LTPA and LTPA2 from WebSphere and set cookies back to browser as LTPA and LTPA2.

• We get cookie name SAPTicketCookie and set cookie back to browser as SAPTicket

• Now, we need to move to RH SSO. So, I consider about 2 alternatives:

1. If there is a way to custom RH SSO login page in the same way we did with IDP
2. Host a custom login page then do HTTP POST to RH SSO Server
   (http:///auth/realms//protocol/openid-connect/token)
   get authorization_token, from respond JSON, do the rest of HTTP POST to get cookie, then set authorization header and cookies back to browser.