build: add typings for additional query params for auth (#1534)

* build: initial implementation of additional query params for auth

---------

Co-authored-by: Daniel Bankhead <danielbankhead@google.com>

src/auth/oauth2client.ts

@@ -296,6 +296,14 @@ export interface GenerateAuthUrlOpts {
    * must be used with the 'code_challenge' parameter described above.
    */
   code_challenge?: string;
+
+  /**
+   * A way for developers and/or the auth team to provide a set of key value
+   * pairs to be added as query parameters to the authorization url.
+   */
+  [
+    key: string
+  ]: querystring.ParsedUrlQueryInput[keyof querystring.ParsedUrlQueryInput];
 }
 
 export interface AccessTokenResponse {

test/test.oauth2.ts

@@ -74,6 +74,8 @@ describe('oauth2', () => {
         access_type: ACCESS_TYPE,
         scope: SCOPE,
         response_type: 'code token',
+        random: 'thing',
+        another: 'random_thing',
       };
 
       const oauth2client = new OAuth2Client({
@@ -89,6 +91,8 @@ describe('oauth2', () => {
       assert.strictEqual(query.get('scope'), SCOPE);
       assert.strictEqual(query.get('client_id'), CLIENT_ID);
       assert.strictEqual(query.get('redirect_uri'), REDIRECT_URI);
+      assert.strictEqual(query.get('random'), 'thing');
+      assert.strictEqual(query.get('another'), 'random_thing');
       done();
     });