<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_certificate_der(self, filename):
 """ Return the DER coded X.509 certificate from the signature file. :param filename: Signature filename in APK :returns: DER coded X.509 certificate as binary """

        pkcs7message = self.get_file(filename)

        pkcs7obj = cms.ContentInfo.load(pkcs7message)
        cert = pkcs7obj['content']['certificates'][0].chosen.dump()
        return cert