libpq: Specify pass phrase for SSL key

Hi,

I am using libpq to set up an SSL connection to a PostgreSQL server. The
client key is protected by a pass phrase, so when I issue a
PQconnectdb(), I get a prompt stating:

Enter PEM pass phrase:

Instead, I would like to give the user a nice message box, asking for
his/her password. So, how do I 'inject' the right SSL password into the
connection sequence?

Thanks for any help!

Koen