P'etsukh translation question

[Krystyna and Nory Steiger]

Hello everyone,
in my P'etsukh text, there is a room freeing up in collective apartment 12.  All of the other tenants feel they are entitled to it, as does the housing office locksmith, Vania, who wants the room on principle.  He sneaks into the apartment one morning and is confronted in the corridor by two tenants.  When asked how he got in, Vania answers:
-- Так я же первостатейный слесарь, -- лукаво ответил тот, -- передо мной все двери открыты, как перед песней.
    Any ideas out there as to what the last half of his reply refers to, if anything?  Is it a popular saying, proverb, or maybe a play on one?  I can't help thinking I'm missing something that might really affect the translation of what seems otherwise to be a simple phrase.
Any advice?  Thanks, again, in advance,
Krystyna

Krystyna Steiger, PhD
Literary Translation
steiger at can.rogers.com

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