  Web users are increasingly presented with multiple login options, including
password-based login and common web single sign-on (SSO) login options such as
"Login with Google" and "Login with Facebook". There has been little focus in
previous studies on how users choose from a list of login options and how to
better inform users about privacy issues in web SSO systems. In this paper, we
conducted a 200-participant study to understand factors that influence
participants' login decisions, and how they are affected by displaying
permission differences across login options; permissions in SSO result in
release of user personal information to third-party web sites through SSO
identity providers. We compare and report on login decisions made by
participants before and after viewing permission-related information, examine
self-reported responses for reasons related to their login decisions, and
report on the factors that motivated their choices. We find that usability
preferences and inertia (habituation) were among the dominant factors
influencing login decisions. After participants viewed permission-related
information, many prioritised privacy over other factors, changing their login
decisions to more privacy-friendly alternatives. Displaying permission-related
information also influenced some participants to make tradeoffs between privacy
and usability preferences.
