For some test purposes of Chef Server I created a "myopenid" username with capitals in it (http://VirtualConcepts.myopenid.com/), and edited /etc/chef/server.rb:
authorized_openid_providers [ "myopenid.com" ]
authorized_openid_identifiers [ "http://VirtualConcepts.myopenid.com/" ]
Although I could login to myopenid.com with or without capitals in my username, I couldn't login to the Chef Server, so I increased the log level to debug:
~ Checking for http://virtualconcepts.myopenid.com/ for OpenID authorization.
~ checking for valid openid identifier: openid: http://virtualconcepts.myopenid.com/, authorized openids: http://VirtualConcepts.myopenid.com/
~ openid: http://virtualconcepts.myopenid.com/ (String), p: http://VirtualConcepts.myopenid.com/ (String)
~ Sorry, http://virtualconcepts.myopenid.com/ is not an authorized OpenID. - (Merb::ControllerExceptions::Unauthorized)
Changing the configuration to:
authorized_openid_identifiers [ "http://virtualconcepts.myopenid.com/" ]
finally fixed this problem.
It seems there is something going wrong with cases in Chef Server during authentication.