(core) support a wildcard option for ALLOWED_WEBHOOK_DOMAINS

Summary:
Now that webhook payload delivery can be done using a proxy,
it may be desirable to no longer require a set of `ALLOWED_WEBHOOK_DOMAINS`.
This diff allows this variable to be set to `*`. With this setting,
any domain, and both `http` and `https` protocols will now be accepted.

Another possibility would be to default to unchecked
behavior if `ALLOWED_WEBHOOK_DOMAINS` is not set. But this would
introduce a new kind of vulnerability to unconfigured Grist
installations.

Test Plan: switched a test from naming a domain to using `*`

Reviewers: jarek

Reviewed By: jarek

Differential Revision: https://phab.getgrist.com/D3903

app/server/lib/Triggers.ts

@@ -772,6 +772,17 @@ export function isUrlAllowed(urlString: string) {
     return false;
   }
 
+  // Support at most https and http.
+  if (url.protocol !== "https:" && url.protocol !== "http:") {
+    return false;
+  }
+
+  // Support a wildcard that allows all domains.
+  // Allow either https or http if it is set.
+  if (process.env.ALLOWED_WEBHOOK_DOMAINS === '*') {
+    return true;
+  }
+
   // http (no s) is only allowed for localhost for testing.
   // localhost still needs to be explicitly permitted, and it shouldn't be outside dev
   if (url.protocol !== "https:" && url.hostname !== "localhost") {