Hello dongjh,
First you need to create the certificate from the Windows vCenter using the certool utility. The procedure is quite straight forward: Generate a New STS Signing Certificate on a vCenter Windows Installation
After you do that you will need to refresh the certificate: Refresh the Security Token Service Certificate
Remember:
- Take a snpashot and backup before doing the task (PSCs and vCenter Server)
- After the procedure restart the server.
Let us know how it goes.