Hi @SRajana 
You might like to consider using HubSpot Webhook Subscriptions for this use case (via Private Apps). See this documentation: Legacy private apps - HubSpot docs
In response to the additional context you’ve supplied, the “Authentication type” option in HubSpot Workflows (specifically for the webhook action type) is intended solely to be used for external system authentication. The way you handle this authentication will be entirely dependent on your external system (e.g. if your external system does not require any form of request authentication, you won’t need to set the “Authentication type” in your HubSpot Workflow).
HubSpot does offer a request validation security feature, which effectively allows your external application to “validate” the given request originated from HubSpot. This works for webhooks from workflow and webhook subscriptions (via Private App), so you’ll likely want to consider using this feature too.
I hope this proves helpful. Please let me know if you have any follow-up questions.