Accessing other databases with DBLink when leaving user/password empty

Hi,

I have the following problem when trying to access other PostgreSQL
databases with DBLink. I followed the instructions on
http://www.postgresonline.com/journal/index.php?/archives/44-Using-DbLink-to-access-other-PostgreSQL-Databases-and-Servers.html.

My query to get access to another database on the same server looks like
this:

select dblink_connect('1512','host=127.0.0.1 port=5432
dbname=Test user=postgres password=postgres');

select * from dblink('1512','select "Vorname", "Name" from
"PERSONEN"')
AS (Vorname text, Name text);

The question is if it is possible to leave the 'user' and 'password'
empty, so that these are taken from the account I'm currently using, as
described below (taken from the above article).

[...]
Below is an example of querying a database on the same server
and cluster using DbLink. Note if no username and password is
specified, then DbLink connects with whatever account you are
currently using.

It is not possible to connect to the other database when they are empty
and it seems that DBLink can't get them from the currently used account.
Can you please help me with that? Thank you.

Regards,
H. Muster