Custom HTTP headers are commonly used to provide additional information. If any end-user wants to provide additional information when default headers are not enough then they can use a custom header configuration.
For example : authentication / encryption / integrity.
Configuration
We can configure custom HTTP Headers using both Org and Site Webhooks API.
Org Webhooks API: https://api.mist.com/api/v1/orgs/{Org-ID}/webhooks
Site Webhooks API: https://api.mistsys.com/api/v1/sites/{Site_ID}/webhooks
API Details: https://api.mist.com/api/v1/docs/Site#webhooks
See this screenshot for reference:
Valid Header Format
"headers":{
"x-custom-1": "your_custom_header_value1",
"x-custom-2": "your_custom_header_value2"
},
If the header value is wrong, the webhooks will still be delivered and the end point URL will receive the header error information: 
