After a recent upgrade to our Samvera installation, we've been dogged
log-in attempt did not appear to be successful. Please try again" errors in
the IIIF viewing window. When the error occurs, it occurs with everything.
But sometimes everything works. I haven't been able to figure out what's
making things break and work (I have no previous experience with this
viewer) -- any pointers to where I should be looking would be appreciated.