When using a VeriSign OpenID to log into a Stack Exchange site (in a browser), I must first log into the VeriSign site manually. If I don't, all I get is a page explaining that VeriSign won't auto redirect me to their log in page for security reasons.
With a browser, all I do is open another tab and log in, then try again on Stack Exchange.
The app, however, does not let me 'open a tab' to log in. The internal browser used by the SE app does not use cookies from my current phone browser (Chrome).
I was only able to log in by linking my Google account with Stack Exchange, then use that as my log in.