Merge pull request #7141 from PuzzleFlow/uid_should_always_be_string

Ensure that uid in OAuth is a string

lib/gitlab/oauth/user.rb

@@ -67,7 +67,9 @@ module Gitlab
         end
 
         def uid
-          auth.info.uid || auth.uid
+          uid = auth.info.uid || auth.uid
+          uid = uid.to_s unless uid.nil?
+          uid
         end
 
         def email