New answers tagged app
I guess the application pool is running under that user. If you Login to your Site with the same (managed) account the web application is running under, it will identify you as "System Account".
To provision artifacts like site columns, content types etc. in host web using provider hosted add-in (previously app), you need to use CSOM/REST approach. Office PnP has few demo on this. Check below links: SharePoint-Add-In-Recipe-site-columns-and-content-types Core.ContentTypesAndFields ECM.DocumentLibraries
I fixed this issue by changing authentication for the "catchall/app" web from negotiate to NTLM. I´m still not sure what fiddler does so it works, but at least apps work as expected. An error in chrome "Invalid Auth Credentials" pointed me in the right direction.
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