1 files changed, 105 insertions, 0 deletions
diff --git a/lib/gitlab/graphql/authorize/authorize_field_service.rb b/lib/gitlab/graphql/authorize/authorize_field_service.rb
new file mode 100644
index 00000000000..8deff79fc84
--- /dev/null
+++ b/lib/gitlab/graphql/authorize/authorize_field_service.rb
@@ -0,0 +1,105 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module Graphql
+    module Authorize
+      class AuthorizeFieldService
+        def initialize(field)
+          @field = field
+          @old_resolve_proc = @field.resolve_proc
+        end
+
+        def authorizations?
+          authorizations.present?
+        end
+
+        def authorized_resolve
+          proc do |parent_typed_object, args, ctx|
+            resolved_obj = @old_resolve_proc.call(parent_typed_object, args, ctx)
+            authorizing_obj = authorize_against(parent_typed_object)
+            checker = build_checker(ctx[:current_user], authorizing_obj)
+
+            if resolved_obj.respond_to?(:then)
+              resolved_obj.then(&checker)
+            else
+              checker.call(resolved_obj)
+            end
+          end
+        end
+
+        private
+
+        def authorizations
+          @authorizations ||= (type_authorizations + field_authorizations).uniq
+        end
+
+        # Returns any authorize metadata from the return type of @field
+        def type_authorizations
+          type = @field.type
+
+          # When the return type of @field is a collection, find the singular type
+          if type.get_field('edges')
+            type = node_type_for_relay_connection(type)
+          elsif type.list?
+            type = node_type_for_basic_connection(type)
+          end
+
+          Array.wrap(type.metadata[:authorize])
+        end
+
+        # Returns any authorize metadata from @field
+        def field_authorizations
+          Array.wrap(@field.metadata[:authorize])
+        end
+
+        # If it's a built-in/scalar type, authorize using its parent object.
+        # nil means authorize using the resolved object
+        def authorize_against(parent_typed_object)
+          parent_typed_object.object if built_in_type? && parent_typed_object.respond_to?(:object)
+        end
+
+        def build_checker(current_user, authorizing_obj)
+          lambda do |resolved_obj|
+            # Load the elements if they were not loaded by BatchLoader yet
+            resolved_obj = resolved_obj.sync if resolved_obj.respond_to?(:sync)
+
+            check = lambda do |object|
+              authorizations.all? do |ability|
+                Ability.allowed?(current_user, ability, authorizing_obj || object)
+              end
+            end
+
+            case resolved_obj
+            when Array, ActiveRecord::Relation
+              resolved_obj.select(&check)
+            else
+              resolved_obj if check.call(resolved_obj)
+            end
+          end
+        end
+
+        # Returns the singular type for relay connections.
+        # This will be the type class of edges.node
+        def node_type_for_relay_connection(type)
+          type = type.get_field('edges').type.unwrap.get_field('node')&.type
+
+          if type.nil?
+            raise Gitlab::Graphql::Errors::ConnectionDefinitionError,
+              'Connection Type must conform to the Relay Cursor Connections Specification'
+          end
+
+          type
+        end
+
+        # Returns the singular type for basic connections, for example `[Types::ProjectType]`
+        def node_type_for_basic_connection(type)
+          type.unwrap
+        end
+
+        def built_in_type?
+          GraphQL::Schema::BUILT_IN_TYPES.has_value?(node_type_for_basic_connection(@field.type))
+        end
+      end
+    end
+  end
+end