Logic App Webhook authorization failure to subscribe Event Grid topic

Question

Hello,

Context : I am using a HTTP webhook in logic App to receive events from Event Grid custom topic

Problem : The http webhook trigger fails with authorization error trying to subscribe to an existing Event grid Topic, with both authentification methods

1. Adding system assigned managed identity (of Logic App) with Event Grid contributor role :

{

"error": {

"code": "Unauthorized",

"message": "Request must contain one of the following authorization signature: aeg-sas-token, aeg-sas-key. Report '22f56014-e4b5-4c72-aec5-48811250dafe:3:6/18/2024 10:56:51 PM (UTC)' to our forums for assistance or raise a support ticket.",

"details": [{

"code": "Unauthorized",

"message": "Request must contain one of the following authorization signature: aeg-sas-token, aeg-sas-key. Report '22f56014-e4b5-4c72-aec5-48811250dafe:3:6/18/2024 10:56:51 PM (UTC)' to our forums for assistance or raise a support ticket."

}]

}

}

2. Adding Event grid SAS key in the request parameter of Logic App's webhook trigger :

https://myexistingtopic.westeurope-1.eventgrid.azure.net/api/events?aeg-sas-key=mysaskeyHere

{

"error": {

"code": "Unauthorized",

"message": "The request authorization key is not authorized for CUSTOMCOMMONTOPIC.WESTEUROPE-1.EVENTGRID.AZURE.NET. Report '118447cf-3350-4dda-819e-2bb24f3d086a:1:6/19/2024 9:42:49 AM (UTC)' to our forums for assistance or raise a support ticket.",

"details": [{

"code": "Unauthorized",

"message": "The request authorization key is not authorized for CUSTOMCOMMONTOPIC.WESTEUROPE-1.EVENTGRID.AZURE.NET. Report '118447cf-3350-4dda-819e-2bb24f3d086a:1:6/19/2024 9:42:49 AM (UTC)' to our forums for assistance or raise a support ticket."

}]

}

}

Thank you