What does logging in with an external Identity provider (IdP) mean

It basically means that data is being shared between the IdP and the Relying party (RP) (the site you are logging in to)

What data is being shared

At the minimum the IdP sends a unique identifier-code to the RP.

Facebooks minimum is to send the identifier-code, name, image and your friend-list. However locatabl.com only uses identifier-code, name and image. The displayed name and image can then be changed in the settings (under ).

What if you change your mind about sharing things

On (app).locatabl.com: in the ->Deadline->"Delete account" you can delete all store data about you.

In the Facebook settings you can also go in and delete the RP's access to your data.