Integrating BI Publisher with E-Business Suite R12.1.3

I followed document https://docs.oracle.com/cd/E23943_01/bi.1111/e22255/integ_security.htm#BIPAD206  for integrating BI Publisher with E-Business Suite R12.1.3

Please explain session login information (overall end to end connection) . For example:

1. say BI Publisher has user ABC and ABC user exists in EBS R12.1.3 also.

2. when ABC login to XMLSERVER (BI Publisher), then authorization happens through EBS R12.

3. To me, it looks ABC user gets connection as APPS user using DBC file uploaded in BI Publisher

4. But how ABC user information gets resolved as APPS. where does this exists? is there any proxy_user_id for ABC user? Please provide more information in this regard.