1. A method for logging a user into an online host system, the method comprising: receiving a login request from a web browser application of a client device, wherein the login request identifies the online host system; in response to receiving the login request, initiating a single sign-on routine that involves an online third party system; thereafter, obtaining third party user data from the online third party system, wherein the obtained third party user data is associated with the user and is maintained by the online third party system; determining that the obtained third party user data is not mapped to any existing user of the online host system; modifying, at the online host system in accordance with the obtained third party user data, host system records maintained by the online host system, wherein the modifying comprises: in response to the determining that the obtained third party user data is not mapped to any existing user of the online host system, creating a new user profile for the online host system, creating a new host system record linked to the new user profile, and populating the new host system record with at least some of the obtained third party user data; and thereafter, automatically logging the user into the online host system.