Credential Manager is a utility that manages your credentials, i.e. stores your usernames and passwords and private key certificates securely on the hard drive. It also remembers what credentials you want to use for which services. This is convenient, as you do not have to enter your security details every time you invoke a service from a workflow that requires you to authenticate. In this respect, Credential Manager is similar to Password Manager in Firefox or Internet Explorer, or Keychain(Apple’s password management system in Mac OS).
Credential Manager also keeps certificates from trusted services and trusted CAs (that issue certificates to services). This is so that Taverna can open HTTPS connections to a desired secure service when executing a workflow, similar to browsers and Java (see also the question about HTTPS). The first time you start the Taverna Workbench 2.x – it will attempt to copy certificates of all trusted CAs that come bundled with Java. If you have played with these settings in Java and changed the default password for Java’s truststore – Taverna will ask you to enter that password so it can perform the copying. If you have not – Taverna will not bug you and will perform the task silently.