Move up api key auth, reuse for activities

app/controllers/api/activities_controller.rb

+# Provides read-only access to Activities.
 class Api::ActivitiesController < ApiController
-  before_action :set_activity, only: [:show, :response_summary]
-  before_action :require_membership!, only: [:show, :reponse_summary]
-  before_action :api_require_admin!, only: [:index]
+  has_no_activity = [:index]
+
+  # Session-based authentication/authorization
+  before_action :set_activity,        except: has_no_activity
+  before_action :require_membership!, except: has_no_activity
+  before_action :api_require_admin!,  only: has_no_activity
+  skip_before_action :api_require_authentication!, :set_activity, :require_membership!, if: 'request.authorization'
+
+  # Group API-key-based authentication/authorization
+  before_action :api_auth_group_token,    if: 'request.authorization'
+  before_action :set_activity_from_group, if: 'request.authorization'
 
   # GET /api/activities
-  # GET /api/activities.json
   def index
     @activities = Activity.all
   end
 
   # GET /api/activities/1
-  # GET /api/activities/1.json
   def show
   end
 
   # GET /api/activities/1/response_summary
-  # GET /api/activities/1/response_summary.json
   def response_summary
     as = @activity
       .participants
   end
 
   private
-    # Use callbacks to share common setup or constraints between actions.
-    def set_activity
-      @activity = Activity.find(params[:id])
-      @group = @activity.group
-    end
+
+  # Set activity from the :id-parameter
+  def set_activity
+    @activity = Activity.find(params[:id])
+    @group = @activity.group
+  end
+
+  # Set activity from the :id-parameter, and assert that it belongs to the set @group.
+  def set_activity_from_group
+    @activity = Activity.find(params[:id])
+    head :unauthorized unless @activity.group == @group
+  end
 end

app/controllers/api/groups_controller.rb

   skip_before_action :set_group, :require_membership!, :api_require_authentication!, if: 'request.authorization'
 
   # API key based filter (both authenticates and authorizes)
-  before_action :api_auth_token, if: 'request.authorization'
+  before_action :api_auth_group_token, if: 'request.authorization'
 
   # GET /api/groups
   def index
   def set_group
     @group = Group.find(params[:id])
   end
-
-  # Authenticate a request by a 'Authorization: Group xxx'-header.
-  # Asserts that the client meant to pass a Group API key, and then sets the
-  # @group variable from the key's associated group.
-  def api_auth_token
-    words = request.authorization.split(' ')
-    head :unauthorized unless words[0].casecmp('group').zero?
-
-    @group = Group.find_by api_token: words[1]
-    head :unauthorized unless @group
-  end
 end

app/controllers/api_controller.rb

     end
   end
 
+  # Authenticate a request by a 'Authorization: Group xxx'-header.
+  # Asserts that the client meant to pass a Group API key, and then sets the
+  # @group variable from the key's associated group.
+  def api_auth_group_token
+    words = request.authorization.split(' ')
+    head :unauthorized unless words[0].casecmp('group').zero?
+
+    @group = Group.find_by api_token: words[1]
+    head :unauthorized unless @group
+  end
+
   # Require user to be a member of group OR admin, requires @group set
   def require_membership!
     if !current_person.groups.include?(@group) && !current_person.is_admin?