Simplify session create logic for both html and json

app/controllers/sessions_controller.rb

@@ -1,7 +1,7 @@
 class SessionsController < ApplicationController
   disallow_account_scope
   require_unauthenticated_access except: :destroy
-  rate_limit to: 10, within: 3.minutes, only: :create, with:  :rate_limit_exceeded
+  rate_limit to: 10, within: 3.minutes, only: :create, with: :rate_limit_exceeded
 
   layout "public"
 
@@ -9,25 +9,15 @@ class SessionsController < ApplicationController
   end
 
   def create
-    if identity = Identity.find_by_email_address(email_address)
-      magic_link = identity.send_magic_link
+    if magic_link = magic_link_from_sign_in_or_sign_up
+      serve_development_magic_link magic_link
+
+      respond_to do |format|
+        format.html { redirect_to_session_magic_link magic_link }
+        format.json { head :created }
+      end
     else
-      signup = Signup.new(email_address: email_address)
-      if signup.valid?(:identity_creation)
-        magic_link = signup.create_identity if Account.accepting_signups?
-      else
-        head :unprocessable_entity
-        return
-      end
-    end
-
-    serve_development_magic_link magic_link
-
-    respond_to do |format|
-      format.html { redirect_to_session_magic_link magic_link }
-      format.json do
-        head :created
-      end
+      head :unprocessable_entity
     end
   end
 
@@ -37,6 +27,17 @@ class SessionsController < ApplicationController
   end
 
   private
+    def magic_link_from_sign_in_or_sign_up
+      if identity = Identity.find_by_email_address(email_address)
+        identity.send_magic_link
+      else
+        signup = Signup.new(email_address: email_address)
+        if signup.valid?(:identity_creation)
+          signup.create_identity if Account.accepting_signups?
+        end
+      end
+    end
+
     def email_address
       params.expect(:email_address)
     end