So this morning I saw the update thinking that it was going to fix some things in the game so I was excited. I downloaded the update and when I went to sign in with my PTC account it gave me the error unable to authenticate. I figured it was just an error but after multiple tries I gave up. Fast forward a couple hours later and it still doesn't work. I slightly panicked, but upon login into the Pokemon website I was still able to login which means that PTC accounts are still valid. Apparently the new update will not let you login with your PTC account no matter what. I remembered I downloaded Pokemon Go on my iPad and I didn't update it yet so I tried to sign in there. Boom it logged me in. So now I need to get the old version back until this is fixed. I remember a while ago I had a similar issue and was able to get an old version of an app. Here's what I plan to do.
For this to work you need to have a previous backup on iTunes with the older version of the app. If you didn't backup, there's a workaround.
Step 1 : Open up iTunes and stop the syncing process if you have it set to auto.
Step 2 : Delete Pokemon Go Version 1.0.1 from your iPhone.
Step 3 : Click on the Apps in the sidebar and look for the older version.
Step 4 : Drag and drop it on the iPhone/device section in the sidebar.
Step 5 : Sync up and you should be good.
If you don't have a previous backup you're not out of luck. If you have any friends that haven't updated yet you can get it from them. Since you can't sync your phone to their computer they will have to send you the file. To do this they will have to follow these steps.
Step 1 : Click on Apps in iTunes and find Pokemon Go.
Step 2 : Right click and click show in Windows Explorer.
Step 3 : Have them send the .ipa file to you so you get it on your computer.
Step 4 : Drag and drop the .ipa file on your device in iTunes.
Step 5 : Sync up and you should be good.
Also just as a warning. I'm not sure if this applies to iOS .ipa files, but I have heard of people uploading Android apks with malware when Pokemon Go first came out since not everyone was able to download it. Only get the .ipa file from a trusted source.
EDIT : As of 7/13/2016 2:27AM EST PTC is working again on Version 1.0.1 !