Signins are still not working on dev.twitter.com at the moment, however, there should only be one or two reasons for this to cause a problem - access to restricted content (which should not affect the vast majority of non-Twitter employees), or use of the OAuth generator tool. We recommend using another tool like
twurl instead. If you need to access your apps, apps.twitter.com is unaffected.
I don't have any eta for the meta issue to be resolved at the moment - low priority since there are alternatives.