2019独角兽企业重金招聘Python工程师标准>>> 
Step 1:
openssl x509 -in aps_developer_identity.cer -inform DER -out aps_developer_identity.pem -outform PEM
Where aps_developer_identity.cer is the file you download from the portal
Step 2:
openssl pkcs12 -nocerts -out APSCertificates.pem -in APSCertificates.p12
Where APSCertificates.p12 is a file you export from the Mac Keychain. This is critical, you must import the certificate from the portal into keychain. Find it in My Certificates, open the disclosure triangle and highlight both the certificate and the private key, then right click and export them. Give them a password and save them to a p12 file.
Step 3:
openssl pkcs12 -export -in aps_developer_identity.pem -out aps_developer_identity.p12 -inkey APSCertificates.pem
第三步之前用http://www.cnblogs.com/qq78292959/archive/2012/07/16/2593651.html博文中的方法：
openssl pkcs12 -export -in aps_developer_identity.pem -inkey Push_Noenc.pem -certfile Push.certSigningRequest -name "aps_developer_identity" -out aps_developer_identity.p12
老是出现unable to load certificates的错误，就此记录一下，其他的过程请参照上面链接中的博文就可以了