Named Credentials in Managed Package Apex Callout

Question

I am trying to create a managed package that has a callout to a webhook. Very simple use case, when opportunities or accounts change we want our server to be notified.

I have setup some Apex triggers and an Apex class to make the webhook callout. Part of the Apex class is as follows:

public static void callout(String content) {

        if (Test.isRunningTest()) {
            Test.setMock(HttpCalloutMock.class, new Webhook());
        }

        Http h = new Http();

        HttpRequest req = new HttpRequest();
        req.setEndpoint('callout:my_credential');
        req.setMethod('POST');
        req.setHeader('Content-Type', 'application/json');
        req.setBody(content);

        h.send(req);
    }

The named credential "my_credential" exists and simply consists of an external credential that has custom authentication with some headers with values, e.g. "X-My-Key". Very confusingly, it doesn't seem like named credentials can be included in the managed package (since external credentials can't), so part of my planned installation instructions was to have the users manually create the named credentials after install.

This does not work at all - nothing happens. The server never receives any requests, no Apex exception email is generated.

In the scratch org I am using to develop the package, if I modify the class to replace the callout with the hardcoded URL (e.g. req.setEndpoint('https://myserver.com');), the server starts getting requests when objects change.

I have tried replacing callout:my_credential with callout:__my_credential and callout:packagename__my_credential. Nothing - nothing happens in either the scratch org I am using to make the package, nor in a dev edition org I installed the package to for testing.

What am I doing wrong here?

Answer 1

It seems that it is not possible for a managed package to use a named credential that is created outside the managed package's code, as per the documentation:

Managed packages can access only the named credentials and external credentials that are included in or created from the package’s Apex code. If a managed package tries to access non-packaged named credentials and external credentials that a Salesforce admin created in the org, an error occurs.

Perhaps you could dynamically create the named and external credentials (in your post-install script or some post-install admin page)?