Solved: How to authenticate POST requests for a custom connector's webhook trigger?

How to authenticate POST requests for a custom connector's webhook trigger?

Hi all, I'm setting up a custom Power Automate connector to use Webhook Triggers with a webapp I control. My use case is roughly the same as the "Create Webhook Trigger" tutorial:

When the trigger is instantiated and saved in a Power Automate flow, it should generate a webhook URL and register it with my app.
When qualifying events happen within my app, it should send a request to the webhook URL.
When Power Automate receives a request to the webhook URL, it should trigger the flow.

I've configured my connector so that steps 1 and 2 are working:

Power Automate is successfully generating a webhook URL (https://prod-41.westus.logic.azure.com/workflows/...) and sending it to my app's registration endpoint.
My app is sending POST requests to the webhook URL, with a body matching the configured body format.

However, my app is always receiving a 401 response for these requests:

{
 "error": {
 "code": "DirectApiAuthorizationRequired",
 "message": "The request must be authenticated only by Shared Access scheme."
 }
}

I've also tried this with Postman and have been getting the same response. I haven't been able to find any description of requirements for request format beyond the destination URL and payload format. The tutorial only addresses authentication for the webhook registration API (ie, step 1)—not authentication for making the webhook request (step 3)—and I haven't found any mention of webhook authN or authZ elsewhere in the custom connector documentation or troubleshooting page.

Is there some way to authenticate webhook URL requests such that Power Automate will accept them?

Quick Links

Leaderboard > Power Automate