Check and Confirm the following :
1) All the required services are up and running by running the following command :
VCSA : service-control --status --all
Browse to the vCenter Installation path : cd C:\Program Files\VMware\vCenter Server\bin
Run the command : service-control --status --all
2) 403 Forbidden error is while accessing the vCenter UI or is it after you enter the user credentials ?
3) Restart the vCenter Services and then check the behavior.
service-control --stop --all
service-control --start --all
Please check the service health status by running the below command,
service-control --status --all
I have a couple of questions here,
1. Is this a freshly installed VC or it was all working well and suddenly started hitting this issue?
2. When are you hitting this issue while opening VC WebClient or while redirecting to SSO?
As suggested by @Ank_S you should try restarting the services and check