Show error on failed OAuth account link

2 files changed, 20 insertions, 4 deletions

diff --git a/lib/gitlab/auth/o_auth/identity_linker.rb b/lib/gitlab/auth/o_auth/identity_linker.rb
index cfa83ba2a55..704a7e1b3c2 100644
--- a/lib/gitlab/auth/o_auth/identity_linker.rb
+++ b/lib/gitlab/auth/o_auth/identity_linker.rb
@@ -3,11 +3,23 @@ module Gitlab
     module OAuth
       class IdentityLinker < OmniauthIdentityLinkerBase
         def create_or_update
-          current_user.identities
-                      .with_extern_uid(oauth['provider'], oauth['uid'])
-                      .first_or_create(extern_uid: oauth['uid'])
+          if identity.new_record?
+            @created = identity.save
+          end
+        end
+
+        def error_message
+          identity.validate
+
+          identity.errors.full_messages.join(', ')
+        end
+
+        private
 
-          @created = true
+        def identity
+          @identity ||= current_user.identities
+                        .with_extern_uid(oauth['provider'], oauth['uid'])
+                        .first_or_initialize(extern_uid: oauth['uid'])
         end
       end
     end
diff --git a/lib/gitlab/auth/omniauth_identity_linker_base.rb b/lib/gitlab/auth/omniauth_identity_linker_base.rb
index c60d9f70a99..4ed28d6a8be 100644
--- a/lib/gitlab/auth/omniauth_identity_linker_base.rb
+++ b/lib/gitlab/auth/omniauth_identity_linker_base.rb
@@ -13,6 +13,10 @@ module Gitlab
         @created
       end
 
+      def error_message
+        ''
+      end
+
       def create_or_update
         raise NotImplementedError
       end