Please, re-open this and fix it!
In the Manage Jenkins/Configure System there should be a whole section for authentication. There's so many goodie links which aren't properly linked in the web interface. There's also no way for one to edit their Oracle credentials for downloading SDK-s. I think there should be a detailed section for the different types of credentials.
Clearly, you can delete the credentials in the respective XML files, but why have to do it manually...?
Apart from this, I somewhat don't agree with the idea of adding the links in the help section. Help and docs are great, but – why have to Google around or read the help when things could be more intuitive? The web interface has become fantastic over the last 10-15 builds. Very quick and responsive. Rather intuitive. This would make things even smoother. 
Subversion credentials are shared across projects, and therefore it is not
necessarily something that every project needs to worry about. For example in a
typical corporate intranet set up, once the system admin enters a credential,
all the jobs can simply reuse the same.
That's the motivation behind the current design — it asynchronously checks the
connectivity and if the credential is necessary it asks you to enter one.
So at least in theory you won't have to find
/hudson/scm/SubversionSCM/enterCredential. I'd like to better understand why you
had to look for that.
I can relatively easily add the link to enterCredential page in
/hudson/configure if you think that's useful.