Change the certification format on iOS from 'cer' to 'der'

[ramosdevgrid]

According to the documentation https://developer.apple.com/documentation/security/1396073-seccertificatecreatewithdata?language=objc The method 'SecCertificateCreateWithData' only accepts '.der' format. If used with '.cer' a null value is returned. To transform a '.cer' to '.der', just call: 'openssl x509 -outform der -in filename.cer -out filename.der'