More interesting than watching paint dry! No, really!
From your vRA appliance, you can see the request go out from /var/log/vcac/catalina.out
Look for com.vmware.identity.websso.client.endpoint.SsoRequestSender.getRequestUrl
On the vRA Identity appliance, look in /var/log/vmware/sso for a localhost_access_log.
check the vmware-sts-idmb.log file on the Identity appliance for the result. You should see an [IdentityManager] entry for the user making the request and the tenant they belong to. Note that the vmware-sts-idmb.log time stamps are in Zulu time so you’ll need to check your math there.