Legacy SSO Credential POST

I know, I know it’s bad but during a transition phase I interested to know what the best option would be to form post to multiple endpoints during login to mimic SSO across sites.

Currently using F5 APM which supports this and I would like to “Initially” find a way to do this.

I assumed this might be done by “Rules” but it seems that the credentials are by then so I can’t leverage them. The other option looked like customising the login page but that seems unwise and clunky. I know Auth0 does something similar with automated migration but i can’t see how I would leverage this.

Is there a way to use hooks/rules to post the credentials to x number of sites after initial login but with the credentials?