Apple Developer Program membership is required to request, download, and use signing certificates issued by Apple. You must also be the Team Agent or an admin of your development team to request distribution certificates used for submitting apps to the App Store or Mac App Store. For more information on how to use signing certificates, review the App Distribution Guide.
In most cases, Xcode is the preferred method to request and install digital certificates for iOS and OS X. However, to request certificates for the Apple Push Notification service, Passbook, Mobile Device Management (MDM), and Safari extensions, you will need to request and download them from Certificates, Identifiers & Profiles in your account on the developer website.