Misleading error message when creating a webhook connector with invalid URL

[luizgpsantos]

Kibana version:

7.7.1

Elasticsearch version:

7.7.1

Server OS version:

macOS Mojave 10.14.6

Browser version:

Google Chrome Version 83.0.4103.61 (Official Build) (64-bit)

Original install method (e.g. download page, yum, from source, etc.):

Downloaded tar.gz from the download page.

Describe the bug:

When creating a Webhook connector in "Alerts and Actions" page, it requires the protocol (http://, https://). Providing the following value example.com/do-something results in an error message that isn't intuitive (xpack.actions.whitelistedHosts defaults to [*]):

error validating action type config: error configuring webhook action: 
target url "example.com/do-something" is not whitelisted in the Kibana
config xpack.actions.whitelistedHosts

Steps to reproduce:

1. Go to Management --> Alerts and Actions --> Connectors --> Create connector;
2. Choose "Webhook" connector;
3. Provide a "Connector name" and type "example.com/do-something" in the URL field;
4. Click in "Save";
5. Check the validation error message.

Expected behavior:

I think there are some options when using example.com/do-something for URL:

• Kibana could infer the http:// protocol;
• Or Kibana could provide a more intuitive error message "Invalid URL, please inform the protocol"
• Any other?

Screenshots (if relevant):

[elasticmachine]

Pinging @elastic/kibana-alerting-services (Team:Alerting Services)

[pmuellr]

We have two different types of action params you can whitelist - URLs (used in most cases in our actions) and host names (used at least by the email action). The URL whitelisting code seems to be generating this non-intuitive message. Seems like it should be doing a bit more work to validate the URL before doing the whitelist check, if that's what's happening. Eg, I'd expect a URL without a protocol to generate a message indicating the URL didn't provide a protocol, in this case.

I'm hoping we can use (one of) Node's built-in URL object(s) to do a validation that would provide a reasonable error message that we can eventually display in the UI.