Retrieves an existing push subscription

Arguments

• scope - Site scope string

Returns

A Subscription response that includes the following:

• A URL that can be used to deliver push messages

• A cryptographic key that can be used to encrypt messages that would then be decrypted using the `PushManager::decrypt` function

Errors

Returns an error in the following cases:

• PushManager was unable to access its persisted storage

• An error occurred generating or deserializing the cryptographic keys