When attempting to request an authenticated user session,

get_authenticated_session() may need to prompt for credentials. It

checks if stdin is a TTY before doing this, and if not, it attempts to

provide an error.
In practice, this originally led to a crash in APIError string

building, which has been fixed in /r/12244/. This change further refines

this reworking the error message to be a bit more friendly and helpful,

less technical, and to place that error in the exception rather than the

log output.
Unfortunately, this error (and authentication prompt logic) exists in

two places: get_authenticated_session() and

Command.credentials_prompt(). Both have been updated, but this change

isn't going to tackle consolidating these code paths.

Triggered this code path and saw a more helpful error message, without a

crash.
Tested the Win32 and non-Win32 versions of this message.