APNs certificates expire annually, so a new certificate must be uploaded to Airship every year upon renewal. This process can take a lot of time if you have multiple Airship projects, and you cannot send messages to your iOS users if your certificate is expired.
Token-based authentication is a one-time configuration in Airship — no more expiration dates! Tokens also give you access control: you can revoke a token in your Apple Developer account at any time.
We recommend updating your projects to use token-based authentication, though we continue to support the certificate method. When configuring iOS in Settings » Channels » Mobile App or Settings » Quickstart Guide, you will now see Token-based authentication in addition to the certificate option.