Get the oracle userid? Make a passthrough query (let's call it "dboOracleUsername") that "passes through" to oracle, and then put in the following SQL:
[tt]GET USER FROM DUAL;[/tt]
that, or SELECT user from DUAL. That query will return one row, called "USER", with the currently-logged on userid.
You then, uh, "query" dboOracleUsername to get their userid. Implementation details are ... details, from this point.