The server certificates and corresponding keys are encrypted by KMS and stored on GCS. This allows us to easily replace expiring certs without having to roll out a new proxy release. However currently the certificate is obtained as a singleton and used in all connections served by a proxy instance. This means that if we were to upload a new cert, all existing instances will not use it.
This CL makes it so that we only cache the certificate for 30 min, after which a new cert is fetched and decrypted. Local certificates used for testing are still singletons.
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