How to extract the contents of a jarsigner-created META-INF/CERT.RSA with PHP?

Question

I specifically want to determine the expiration date of the key used to sign an Android APK.

The file appears to be DER-encoded PKCS#7, as this shows me the contents:

openssl pkcs7 -inform DER -in CERT.RSA -noout -print_certs -text

Some approaches I have tried:

/* try to open as pkcs#7.  prints FALSE. */

if( TRUE === openssl_pkcs7_verify ( 'CERT.RSA', 0 ) ) {
    echo "TRUE\n";
}
else {
    echo "FALSE\n";
}

/* try to open as an x509.  prints FALSE. */

$data = openssl_x509_parse(file_get_contents('CERT.RSA'));
if( $data === FALSE ) {
    echo "FALSE\n";
}

/*                                                                                                         
   un-DER with phpseclib                                                                                   

   prints a nestated data structure that clearly includes                                                  
   data from CERT.RDA, but unclear to me which value is                                                    
  the cert expiration date.                                                                               
*/

$ASN1 = new File_ASN1(file_get_contents('CERT.RSA'));
print_r( $ASN1->decodeBER(file_get_contents('CERT.RSA')) );`

I could just call openssl from an exec() or similar, but I'd rather have a pure-PHP solution. Anybody got one?