(core) implement authorization via query parameter

Summary:
This adds any parameters in a document url whose key ends in '_'
into a `user.Link` object available in access control formulas
and in setting up characteristic tables.

This allows, for example, sending links to a document that contain
a hard-to-guess token, and having that link grant access to a
controlled part of the document (invoices for a specific customer
for example).

A `user.Origin` field is also added, set during rest api calls,
but is only tested manually at this point.  It could be elaborated
for embedding use-cases.

Test Plan: added test

Reviewers: dsagal

Reviewed By: dsagal

Differential Revision: https://phab.getgrist.com/D2680

app/client/components/Comm.ts

@@ -267,8 +267,9 @@ export class Comm extends dispose.Disposable implements GristServerAPI, DocListA
    * committed to a document that is called in hosted Grist - all other methods
    * are called via DocComm.
    */
-  public async openDoc(docName: string, mode?: string): Promise<OpenLocalDocResult> {
-    return this._makeRequest(null, docName, 'openDoc', docName, mode);
+  public async openDoc(docName: string, mode?: string,
+                       linkParameters?: Record<string, string>): Promise<OpenLocalDocResult> {
+    return this._makeRequest(null, docName, 'openDoc', docName, mode, linkParameters);
   }
 
   /**

app/client/components/DocComm.ts

@@ -189,6 +189,7 @@ export class DocComm extends Disposable implements ActiveDocAPI {
   private async _doForkDoc(): Promise<void> {
     reportError(new UserError('Preparing your copy...', {key: 'forking'}));
     const {urlId, docId} = await this.fork();
+    // TODO: may want to preserve linkParameters in call to openDoc.
     const openResponse = await this._comm.openDoc(docId);
     // Close the old doc and release the old connection. Note that the closeDoc call is expected
     // to fail, since we close the websocket immediately after it. So let it fail silently.