Implemented issue #1954 - Allow to automatically linking of existing user by initial login via third party authentication provider.

app/models/authorization.rb

@@ -53,6 +53,12 @@ class Authorization < ApplicationModel
 
   def self.create_from_hash(hash, user = nil)
 
+    if !user && Setting.get('auth_third_party_auto_link_at_inital_login')
+      if hash['info'] && hash['info']['email'].present?
+        user = User.find_by(email: hash['info']['email'].downcase)
+      end
+    end
+
     if !user
       user = User.create_from_hash!(hash)
     end

app/models/user.rb

@@ -386,7 +386,7 @@ returns
       next if local_url.blank?
       url = local_url
     end
-    create(
+    create!(
       login: hash['info']['nickname'] || hash['uid'],
       firstname: hash['info']['name'],
       email: hash['info']['email'],

db/migrate/20180418000001_setting_third_party_link_account_at_login.rb

@@ -0,0 +1,34 @@
+class SettingThirdPartyLinkAccountAtLogin < ActiveRecord::Migration[5.1]
+  def up
+
+    # return if it's a new setup
+    return if !Setting.find_by(name: 'system_init_done')
+
+    Setting.create_if_not_exists(
+      title: 'Automatic account link on initial logon',
+      name: 'auth_third_party_auto_link_at_inital_login',
+      area: 'Security::ThirdPartyAuthentication',
+      description: 'Enables the automatic linking of an existing account on initial login via a third party application. If this is disabled, an existing user must first log into Zammad and then link his "Third Party" account to his Zammad account via Profile -> Linked Accounts.',
+      options: {
+        form: [
+          {
+            display: '',
+            null: true,
+            name: 'auth_third_party_auto_link_at_inital_login',
+            tag: 'boolean',
+            options: {
+              true  => 'yes',
+              false => 'no',
+            },
+          },
+        ],
+      },
+      preferences: {
+        permission: ['admin.security'],
+        prio: 10,
+      },
+      state: false,
+      frontend: false
+    )
+  end
+end

db/seeds/settings.rb

@@ -954,6 +954,32 @@ Setting.create_if_not_exists(
   },
   frontend: false
 )
+Setting.create_if_not_exists(
+  title: 'Automatic account link on initial logon',
+  name: 'auth_third_party_auto_link_at_inital_login',
+  area: 'Security::ThirdPartyAuthentication',
+  description: 'Enables the automatic linking of an existing account on initial login via a third party application. If this is disabled, an existing user must first log into Zammad and then link his "Third Party" account to his Zammad account via Profile -> Linked Accounts.',
+  options: {
+    form: [
+      {
+        display: '',
+        null: true,
+        name: 'auth_third_party_auto_link_at_inital_login',
+        tag: 'boolean',
+        options: {
+          true  => 'yes',
+          false => 'no',
+        },
+      },
+    ],
+  },
+  preferences: {
+    permission: ['admin.security'],
+    prio: 10,
+  },
+  state: false,
+  frontend: false
+)
 Setting.create_if_not_exists(
   title: 'Authentication via %s',
   name: 'auth_twitter',