Just in case I will need it the next time ... This article is a good description how to
- Adding trusted root and intermediary certificates to the Cell default trust store
- Generating a certificate signer request
- Installing a signed certificate
- Configuring the servers to use the signed certificate
Although the article is written for Lotus sametime in can be used for other Websphere servers as well.
Websphere: Replacing the default IBM self-signed certificate with another certificate