Hi, Gerhard.
I assume you imply usage of SAML protocol in your setup, please correct me otherwise. You may need to contact your SP tech support (or consult its documentation) to figure out what options do you have, Gluu Server has little control over how SP does its part of job. Usually SAML response is returned to SP by POSTing it to pre-defined ACS, and from there it's up to SP what to do.
The most known way to achieve something like this is by utilizing [RelayState parameter](https://stackoverflow.com/questions/34350160/what-is-exactly-relaystate-parameter-used-in-sso-ex-saml). But its support and usage is implementaion-dependend, so you'll need to research your case a bit more. In its simplest form `RelayState` passed in urq query string of SAML request contains url of a resource user needs to be redirected to after authentication. Then IDP should mirror it in its response to SP, and SP is expected to send user there.
Unfortunately, Community support doesn't cover SP configuration, so you'll have to find the answer yourself. Feel free to share it here afterwards, for others to learn up.