code: public ApnsServiceBuilder withCert(String fileName, String password)
      throws RuntimeIOException, InvalidSSLConfig {
          FileInputStream stream = null;
          try {
              stream = new FileInputStream(fileName);
              return withCert(stream, password);
          } catch (FileNotFoundException e) {
              throw new RuntimeIOException(e);
          } finally {
              Utilities.close(stream);
          }
      }
docs: Specify the certificate used to connect to Apple APNS
  servers.  This relies on the path (absolute or relative to
  working path) to the keystore (*.p12) containing the
  certificate, along with the given password.
  
  The keystore needs to be of PKCS12 and the keystore
  needs to be encrypted using the SunX509 algorithm.  Both
  of these settings are the default.
  
  This library does not support password-less p12 certificates, due to a
  Oracle Java library <a href="http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6415637">
  Bug 6415637</a>.  There are three workarounds: use a password-protected
  certificate, use a different boot Java SDK implementation, or construct
  the `SSLContext` yourself!  Needless to say, the password-protected
  certificate is most recommended option.
  
  @param fileName  the path to the certificate
  @param password  the password of the keystore
  @return  this
  @throws RuntimeIOException if it {@code fileName} cannot be
  found or read
  @throws InvalidSSLConfig if fileName is invalid Keystore
  or the password is invalid