diff --git a/config/config.example.yml b/config/config.example.yml
index 47a17c4f..cf8d9d05 100644
--- a/config/config.example.yml
+++ b/config/config.example.yml
@@ -562,6 +562,17 @@ log:
 #enable_single_sign_out: true
 
 
+##### SERVICES #################################################################
+
+# You can restrict what services can authenticate against the CAS server.
+
+# By default any service can authenticate and a blank white list will also
+# allow any service to authenticate. Services are listed on a single line
+# separated by a comma.
+
+#service_whitelist: https://service.one.com,https://service.two.com
+
+
 ##### OTHER ####################################################################
 
 # You can set various ticket expiry times (specify the value in seconds).
diff --git a/lib/casserver/server.rb b/lib/casserver/server.rb
index 12d1f756..73880780 100644
--- a/lib/casserver/server.rb
+++ b/lib/casserver/server.rb
@@ -293,6 +293,7 @@ def self.init_database!
         require @template_engine
         @template_engine = @template_engine.to_sym
       end
+      @service_whitelist = CASServer::Utils::initialize_service_whitelist(settings.config[:service_whitelist])
     end
 
     # The #.#.# comments (e.g. "2.1.3") refer to section numbers in the CAS protocol spec
@@ -310,7 +311,7 @@ def self.init_database!
       headers['Expires'] = (Time.now - 1.year).rfc2822
 
       # optional params
-      @service = clean_service_url(params['service'])
+      @service = CASServer::Utils::validate_service(clean_service_url(params['service']), @service_whitelist)
       @renew = params['renew']
       @gateway = params['gateway'] == 'true' || params['gateway'] == '1'
 
@@ -400,7 +401,7 @@ def self.init_database!
       Utils::log_controller_action(self.class, params)
       
       # 2.2.1 (optional)
-      @service = clean_service_url(params['service'])
+      @service = CASServer::Utils::validate_service(clean_service_url(params['service']), @service_whitelist)
 
       # 2.2.2 (required)
       @username = params['username']
@@ -516,7 +517,7 @@ def self.init_database!
       # "logout" page, we take the user back to the login page with a "you have been logged out"
       # message, allowing for an opportunity to immediately log back in. This makes it
       # easier for the user to log out and log in as someone else.
-      @service = clean_service_url(params['service'] || params['destination'])
+      @service = CASServer::Utils::validate_service(clean_service_url(params['service']), @service_whitelist) || clean_service_url(params['destination'])
       @continue_url = params['url']
 
       @gateway = params['gateway'] == 'true' || params['gateway'] == '1'
@@ -607,7 +608,7 @@ def self.init_database!
 			CASServer::Utils::log_controller_action(self.class, params)
 			
 			# required
-			@service = clean_service_url(params['service'])
+			@service = CASServer::Utils::validate_service(clean_service_url(params['service']), @service_whitelist)
 			@ticket = params['ticket']
 			# optional
 			@renew = params['renew']
@@ -630,7 +631,7 @@ def self.init_database!
 			CASServer::Utils::log_controller_action(self.class, params)
 
 			# required
-			@service = clean_service_url(params['service'])
+			@service = CASServer::Utils::validate_service(clean_service_url(params['service']), @service_whitelist)
 			@ticket = params['ticket']
 			# optional
 			@pgt_url = params['pgtUrl']
@@ -661,7 +662,7 @@ def self.init_database!
       CASServer::Utils::log_controller_action(self.class, params)
 
       # required
-      @service = clean_service_url(params['service'])
+      @service = CASServer::Utils::validate_service(clean_service_url(params['service']), @service_whitelist)
       @ticket = params['ticket']
       # optional
       @pgt_url = params['pgtUrl']
diff --git a/lib/casserver/utils.rb b/lib/casserver/utils.rb
index 324db887..1075c3bf 100644
--- a/lib/casserver/utils.rb
+++ b/lib/casserver/utils.rb
@@ -28,5 +28,22 @@ def log_controller_action(controller, params)
       $LOG.debug("Processing #{controller}::#{method} #{params2.inspect}")
     end
     module_function :log_controller_action
+
+    def initialize_service_whitelist(whitelist)
+      $LOG.debug("Initializing Service Whitelist")
+      whitelist = whitelist || ''
+      whitelist.split(',')
+    end
+    module_function :initialize_service_whitelist
+
+    def validate_service(service, whitelist)
+      $LOG.debug("Validating service \"#{service}\"")
+      return service if whitelist.empty?
+      $LOG.debug("Checking service whitelist")
+      return service if whitelist.include?(service)
+      $LOG.warn("Service \"#{service}\" is not in service whitelist")
+      nil
+    end
+    module_function :validate_service
   end
 end