Add ability to supply a callable error handler

resolves #23

Why?
The scim engine returns a custom response to the caller in the event
that there is a 500 error in the engine. It rescues any standard error
in order to do this.

Unfortunately this means that when something is broken it does not
bubble up to the parent app's error handling system or even be printed
in the logs.

We cannot just re-raise the exception because you cannot return a
response AND raise an exception as a part of the same request.

To help, this PR will make is possible for you to supply a callable
object that take the exception as it's argument.

If no callable object is provided, we will output the exception to the
logs so that silence is not the default.

To get the old behavior of completely ignoring an exception, you could
supply an empty proc.

.gitignore

@@ -5,3 +5,4 @@ spec/dummy/db/*.sqlite3
 spec/dummy/db/*.sqlite3-journal
 spec/dummy/log/*.log
 spec/dummy/tmp/
+.rubocop-https*

.rubocop.yml

@@ -0,0 +1,2 @@
+inherit_from:
+  - https://raw.githubusercontent.com/lessonly/rubocop-default-configuration/master/.rubocop.yml

CHANGELOG.md

@@ -0,0 +1,3 @@
+# Upcoming Release
+
+- Any unhandled error is now logged to the configured rails logger by default. You can also now supply a custom callable that will be used to handle those exceptions instead.

README.md

@@ -246,6 +246,20 @@ Sample request:
 $ curl -X PATCH 'http://username:password@localhost:3000/scim/v2/Users/1' -d '{"schemas": ["urn:ietf:params:scim:api:messages:2.0:PatchOp"], "Operations": [{"op": "replace", "value": { "active": false }}]}' -H 'Content-Type: application/scim+json'
 ```
 
+### Error Handling
+
+By default, scim_rails will output any unhandled exceptions to your configured rails logs.
+
+If you would like, you can supply a custom handler for exceptions in the initializer. The only requirement is that the value you supply responds to `#call`.
+
+For example, you might want to notify Honeybadger:
+
+```ruby
+ScimRails.configure do |config|
+  config.on_error = ->(e) { Honeybadger.notify(e) }
+end
+```
+
 ## Contributing
 
 ### [Code of Conduct](https://github.com/lessonly/scim_rails/blob/master/CODE_OF_CONDUCT.md)

app/controllers/concerns/scim_rails/exception_handler.rb

@@ -12,12 +12,15 @@ class UnsupportedPatchRequest < StandardError
     end
 
     included do
-      # StandardError must be ordered _first_ or it will catch all exceptions
-      #
-      # TODO: Build a plugin/configuration for error handling so that the
-      # detailed production errors are logged somewhere if desired.
       if Rails.env.production?
-        rescue_from StandardError do
+        rescue_from StandardError do |exception|
+          on_error = ScimRails.config.on_error
+          if on_error.respond_to?(:call)
+            on_error.call(exception)
+          else
+            Rails.logger.error(exception.inspect)
+          end
+
           json_response(
             {
               schemas: ["urn:ietf:params:scim:api:messages:2.0:Error"],

lib/scim_rails/config.rb

@@ -1,26 +1,32 @@
+# frozen_string_literal: true
+
 module ScimRails
   class << self
     def configure
       yield config
     end
 
     def config
-      @_config ||= Config.new
+      @config ||= Config.new
     end
   end
 
+  # Class containing configuration of ScimRails
   class Config
-    ALGO_NONE = "none".freeze
+    ALGO_NONE = "none"
 
-    attr_accessor \
+    attr_writer \
       :basic_auth_model,
+      :mutable_user_attributes_schema,
+      :scim_users_model
+
+    attr_accessor \
       :basic_auth_model_authenticatable_attribute,
       :basic_auth_model_searchable_attribute,
       :mutable_user_attributes,
-      :mutable_user_attributes_schema,
+      :on_error,
       :queryable_user_attributes,
       :scim_users_list_order,
-      :scim_users_model,
       :scim_users_scope,
       :scim_user_prevent_update_on_create,
       :signing_secret,