Third-party authentication services are becoming more common since it eases the login procedure by not forcing users to create a new login for every website thatuses authentication. Even though it simplifies the login procedure the users still have to be conscious about what data is being shared between the identity provider (IDP) and the relying party (RP). This thesis presents a tool for collecting data about third-party authentication that outperforms previously made tools with regards to accuracy, precision and recall. The developed tool was used to collect information about third-party authentication on a set of websites. The collected data revealed that third-party login services offered by Facebook and Google are most common and that Twitters login service is significantly less common. Twitter's login service shares the most data about the users to the RPs and often gives the RPs permissions to perform write actions on the users Twitter account.  In addition to our large-scale automatic data collection, three manual data collections were performed and compared to previously made manual data collections from a nine-year period. The longitudinal comparison showed that over the nine-year period the login services offered by Facebook and Google have been dominant.It is clear that less information about the users are being shared today compared to earlier years for Apple, Facebook and Google. The Twitter login service is the only IDP that have not changed their permission policies. This could be the reason why the usage of the Twitter login service on websites have decreased.  The results presented in this thesis helps provide a better understanding of what personal information is exchanged by IDPs which can guide users to make well educated decisions on the web.