added CasrackTheAuthenticator::USERNAME_PARAM and used it as per the …

…README

lib/casrack_the_authenticator.rb

@@ -1,5 +1,7 @@
 module CasrackTheAuthenticator
 
+  USERNAME_PARAM = :cas_user
+
   autoload :Simple, 'casrack_the_authenticator/simple'
   autoload :Configuration, 'casrack_the_authenticator/configuration'
   autoload :ServiceTicketValidator, 'casrack_the_authenticator/service_ticket_validator'

lib/casrack_the_authenticator/fake.rb

@@ -36,7 +36,7 @@ def call(env)
     def process_basic_auth(env)
       auth = Rack::Auth::Basic::Request.new(env)
       if auth.provided? && auth.basic? && @usernames.include?(auth.username)
-        Rack::Request.new(env).session[:cas_user] = auth.username
+        Rack::Request.new(env).session[CasrackTheAuthenticator::USERNAME_PARAM] = auth.username
       end
     end
 

lib/casrack_the_authenticator/require_cas.rb

@@ -23,7 +23,7 @@ def call(env)
 
     # @return [true, false] whether the user is signed in via CAS.
     def signed_in?(env)
-      !Rack::Request.new(env).session[:cas_user].nil?
+      !Rack::Request.new(env).session[CasrackTheAuthenticator::USERNAME_PARAM].nil?
     end
 
     # @return [Array<Integer, Hash, String>] a 401 Unauthorized Rack response.

lib/casrack_the_authenticator/simple.rb

@@ -41,7 +41,7 @@ def process_return_from_cas(request)
         ticket = request.params['ticket']
         if ticket
           validator = ServiceTicketValidator.new(@configuration, service_url(request), ticket)
-          request.session[:cas_user] = validator.user
+          request.session[CasrackTheAuthenticator::USERNAME_PARAM] = validator.user
         end
       end