I got it working by adding the 1.0.6 dependency in the devise_case_authenticable gemspec file /usr/local/rvm/gems/ruby-1.9.3-p551/bundler/gems/snorby_cas_authenticatable-281a58b36368/devise_cas_authenticatable.gemspec:
if s.respond_to? :specification_version then
s.specification_version = 3
if Gem::Version.new(Gem::VERSION) >= Gem::Version.new('1.2.0') then
s.add_runtime_dependency(%q<devise>, [">= 0"])
s.add_development_dependency(%q<ruby-debug>, [">= 0"])
s.add_development_dependency(%q<jeweler>, [">= 0"])
**s.add_runtime_dependency(%q<devise>, [">= 1.0.6"])**
s.add_runtime_dependency(%q<rubycas-client>, [">= 2.2.1"])
else
s.add_dependency(%q<devise>, [">= 0"])
s.add_dependency(%q<ruby-debug>, [">= 0"])
s.add_dependency(%q<jeweler>, [">= 0"])
**s.add_dependency(%q<devise>, [">= 1.0.6"])**
s.add_dependency(%q<rubycas-client>, [">= 2.2.1"])
end
else
s.add_dependency(%q<devise>, [">= 0"])
s.add_dependency(%q<ruby-debug>, [">= 0"])
s.add_dependency(%q<jeweler>, [">= 0"])
**s.add_dependency(%q<devise>, [">= 1.0.6"])**
s.add_dependency(%q<rubycas-client>, [">= 2.2.1"])
end
end
and then changing
gem 'devise_cas_authenticatable', :git => 'https://github.com/Snorby/snorby_cas_authenticatable.git'
in the Snorby gemfile in the snorby www root to
gem 'devise_cas_authenticatable'
My guess is that this will only work after if failing once, so that the devise_cas_authenticable gem is installed