Identity Provider (IDP)
The information about integrating BCSC login with the application can be found in this discussion.
GUID is Globally unique identifier and the identity partners we work with (IDIR and BCeID), make use of a SAML protocol. Accordingly certain user attributes are sent with a "payload" and one of those attributes is the GUID.
Please refer to the following discussion for the similar question.
Personal BCeID is now being deprecated by the IDIM team; they discourage use of it and are actively trying to move teams using it to use BC Services Card