question

If you use “Function” level authentication for Azure Functions, there will be an API key that can used to authenticate callers of your Azure Functions. This authentication key is a concept of the Azure Functions and not related to PlayFab developer secret key. PlayFab Secret key is only for Server/Admin API, or getting a title-level entity token, you can store it at configuration page of Azure portal for later reference.

You can check the documentations of Azure Functions, specifically this documentation - Azure Functions HTTP trigger | Microsoft Docs for more information about different types of auth levels and the corresponding examples.

As this section - API key authorization mentioned, if you set up the Azure Functions with the API key. The URL of your function could be something like this.

https://<APP_NAME>.azurewebsites.net/api/<FUNCTION_NAME>?code=<API_KEY>

To register the Azure Functions that using “Function” level authentication, you just need to paste the URL that contains the above “code” to PlayFab. If you upload your azure function with “function” method, the function URL you get from Azure contains API keys. The advantage of using “function” method is to avoid abusive or anonymous calls because Azure Function is metered by usage.

If you have any other technical questions about how to set up “functions” authentication for your Azure Functions, please refer to the above Azure Functions documentations or follow this page - Azure Support Options | Microsoft Azure to contact the technical supports of Azure for more professional help.