Apple Push notification in a production environment: local issuer certificate cannot be obtained

Question

I applied APNS push notification on my server using the development certificate for my application. It works fine until I try to change the certificate to a Push certificate.

I am trying to test the connection with:

openssl s_client -connect gateway.push.apple.com:2195 -cert myCert.pem -key myKey.pem 

After entering the correct password, a summary is displayed:

 New, TLSv1/SSLv3, Cipher is AES256-SHA Server public key is 2048 bit Secure Renegotiation IS supported Compression: NONE Expansion: NONE SSL-Session: Protocol : TLSv1 Cipher : AES256-SHA Session-ID: Session-ID-ctx: Master-Key: FB8BCFEA572E9C75330E15C11945D35F681C9561136FB0FCA42C9FE3E96E1E73E7D4EF255CC1AE94AF947D69D3CEEFC7 Key-Arg : None Start Time: 1342426207 Timeout : 300 (sec) Verify return code: 20 (unable to get local issuer certificate) 

However, on my local computer, the same command returns:

 New, TLSv1/SSLv3, Cipher is AES256-SHA Server public key is 2048 bit Secure Renegotiation IS supported Compression: NONE Expansion: NONE SSL-Session: Protocol : TLSv1 Cipher : AES256-SHA Session-ID: Session-ID-ctx: Master-Key: A08BDD17603F062305F47EBC36B55DC03CED501B6C03CFBDEFFB519E5F1586DF2CCC689816AA0C18C19931D7FE2DF85F Key-Arg : None Start Time: 1342422311 Timeout : 300 (sec) Verify return code: 0 (ok) 

What did I miss? Do I need to change anything in my PHP codes?

I suspect that I need to install the Apple Worldwide Developer Authority intermediate certificate on my Ubuntu server, but am not entirely sure.