(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/FlexServer.ts

@@ -1325,6 +1325,22 @@ export class FlexServer implements GristServer {
     }
   }
 
+  public checkOptionCombinations() {
+    // Check for some bad combinations we should warn about.
+    const allowedWebhookDomains = appSettings.section('integrations').flag('allowedWebhookDomains').readString({
+      envVar: 'ALLOWED_WEBHOOK_DOMAINS',
+    });
+    const proxy = appSettings.section('integrations').flag('proxy').readString({
+      envVar: 'GRIST_HTTPS_PROXY',
+    });
+    // If all webhook targets are accepted, and no proxy is defined, issue
+    // a warning. This warning can be removed by explicitly setting the proxy
+    // to the empty string.
+    if (allowedWebhookDomains === '*' && proxy === undefined) {
+      log.warn("Setting an ALLOWED_WEBHOOK_DOMAINS wildcard without a GRIST_HTTPS_PROXY exposes your internal network");
+    }
+  }
+
   public async start() {
     if (this._check('start')) { return; }
 

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") {

app/server/mergedServerMain.ts

@@ -141,6 +141,7 @@ export async function main(port: number, serverTypes: ServerType[],
 
   server.finalize();
 
+  server.checkOptionCombinations();
   server.summary();
   return server;
 }