Expose a method for encrypting using a remote v2_key

app/models/miq_region.rb

@@ -290,29 +290,33 @@ def auth_key_configured?
   end
 
   def api_system_auth_token(userid)
-    region_v2_key = authentication_token(AUTHENTICATION_TYPE)
-
     token_hash = {
       :server_guid => remote_ws_miq_server.guid,
       :userid      => userid,
       :timestamp   => Time.now.utc
     }
+    encrypt(token_hash.to_yaml)
+  end
+
+  def required_credential_fields(_type)
+    [:auth_key]
+  end
+
+  def encrypt(string)
+    region_v2_key = authentication_token(AUTHENTICATION_TYPE)
+    raise "No key configured for region #{region}. Configure Central Admin to fetch the key" if region_v2_key.nil?
 
     file = Tempfile.new("region_auth_key")
     begin
       file.write(region_v2_key)
       file.close
       key = EzCrypto::Key.load(file.path)
-      MiqPassword.new.encrypt(token_hash.to_yaml, "v2", key)
+      MiqPassword.new.encrypt(string, "v2", key)
     ensure
       file.unlink
     end
   end
 
-  def required_credential_fields(_type)
-    [:auth_key]
-  end
-
   def self.api_system_auth_token_for_region(region_id, user)
     find_by_region(region_id).api_system_auth_token(user)
   end

spec/models/miq_region_spec.rb

@@ -238,6 +238,24 @@
     end
   end
 
+  describe "#encrypt" do
+    let(:region) { FactoryGirl.create(:miq_region, :region => ApplicationRecord.my_region_number) }
+
+    it "correctly encrypts a string using the authentication token" do
+      expect(region).to receive(:authentication_token).and_return(File.read(Rails.root.join("certs/v2_key")))
+
+      a_string = "this should be encrypted correctly"
+      enc = region.encrypt(a_string)
+      other_string = MiqPassword.decrypt(enc)
+
+      expect(other_string).to eq(a_string)
+    end
+
+    it "raises if no key is configured" do
+      expect { region.encrypt("a string") }.to raise_error(RuntimeError)
+    end
+  end
+
   context "ConfigurationManagementMixin" do
     let(:region) { FactoryGirl.create(:miq_region, :region => ApplicationRecord.my_region_number) }