Hello Nwa d - thank you for your question and welcome to our community!
It’s common practice that Ausländerbehörde keeps your passport for the duration of your asylum procedure.
You are in Germany to ask for asylum because your country of origin is not able or willing to provide you with shelter. If you seek protection from your home country then there is no more reason for German authorities to give you asylum. On the one hand that’s why they won’t ask you to get in contact with your home country’s embassy during the procedure. On the other hand your claim for shelter in Germany expires if you apply for a new passport issued by your country of origin on your own accord. That’s why I won’t recommend you to get in touch with them in order to get a new passport.
Source (German language): http://www.fluechtlingsrat-bayern.de/tl_files/BLEIB%20IN%20BAYERN/Dokumente/Rundschreiben%20Passbeschaffung%20aktualisiert%20Stand%2027.06.17.pdf
Maybe you can ask Standesamt if they would accept other documents than a passport like a certificate of nationality in combination with another proof of identity. I found a source online that states that an expired passport could be sufficient to marry as well (German language): http://www.schutzehe.com/data/de_data/de_leitfaden.htm