PubSub component authentication works with
Google IAM Service Accounts
and two-legged OAuth, in order to authenticate your component you would
need to create a new Service Account on Service Accounts Page
of your project and download the JSON file with the private key.
You would need
on component authentication page (see here
for more information).
Please take a special care of the indepmotency of your processing flow, here is the extract from PubSub Subscriber Guide
For the most part Pub/Sub delivers each message once, and in the order in which it was published. However, once-only and in-order delivery are not guaranteed: it may happen that a message is delivered more than once, and out of order. Therefore, your subscriber should be idempotent when processing messages, and, if necessary, able to handle messages received out of order. If ordering is important, we recommend that the publisher of the topic to which you subscribe include some kind of sequence information in the message; see this page for a full discussion on message ordering. Messages that are not acknowledged, are retried indefinitely for up to seven days.