From b6852df0188992462d6570e992fedd9e777c8d54 Mon Sep 17 00:00:00 2001
From: Daniel Bankhead <danielbankhead@google.com>
Date: Wed, 5 Feb 2025 17:07:23 -0800
Subject: [PATCH] refactor: Use Gaxios Interceptors for default Auth headers

---
 src/auth/authclient.ts  | 77 ++++++++++++++++++++++++-----------------
 test/test.authclient.ts | 28 +++++++++++++++
 2 files changed, 74 insertions(+), 31 deletions(-)

diff --git a/src/auth/authclient.ts b/src/auth/authclient.ts
index 5dc84517..fecb5cda 100644
--- a/src/auth/authclient.ts
+++ b/src/auth/authclient.ts
@@ -83,6 +83,8 @@ export interface AuthClientOptions
 
   /**
    * The {@link Gaxios `Gaxios`} instance used for making requests.
+   *
+   * @see {@link AuthClientOptions.useAuthRequestParameters}
    */
   gaxios?: Gaxios;
 
@@ -106,6 +108,19 @@ export interface AuthClientOptions
    * on the expiry_date.
    */
   forceRefreshOnFailure?: boolean;
+
+  /**
+   * Enables/disables the adding of the AuthClient's default interceptor.
+   *
+   * @see {@link AuthClientOptions.gaxios}
+   *
+   * @remarks
+   *
+   * Disabling is useful for debugging and experimentation.
+   *
+   * @default true
+   */
+  useAuthRequestParameters?: boolean;
 }
 
 /**
@@ -210,6 +225,12 @@ export abstract class AuthClient
     // Shared client options
     this.transporter = opts.gaxios ?? new Gaxios(opts.transporterOptions);
 
+    if (options.get('useAuthRequestParameters') !== false) {
+      this.transporter.interceptors.request.add(
+        AuthClient.DEFAULT_REQUEST_INTERCEPTOR
+      );
+    }
+
     if (opts.eagerRefreshThresholdMillis) {
       this.eagerRefreshThresholdMillis = opts.eagerRefreshThresholdMillis;
     }
@@ -224,37 +245,6 @@ export abstract class AuthClient
    */
   abstract request<T>(options: GaxiosOptions): GaxiosPromise<T>;
 
-  /**
-   * The internal request handler.
-   *
-   * @privateRemarks
-   *
-   * At this stage the credentials have been already prepared - passing it
-   * here adds the standard headers to the request, if not previously configured.
-   *
-   * @param options options for `gaxios`
-   */
-  protected _request<T>(options: GaxiosOptions): GaxiosPromise<T> {
-    const headers = options.headers || {};
-
-    // Set `x-goog-api-client`, if not already set
-    if (!headers['x-goog-api-client']) {
-      const nodeVersion = process.version.replace(/^v/, '');
-      headers['x-goog-api-client'] = `gl-node/${nodeVersion}`;
-    }
-
-    // Set `User-Agent`
-    if (!headers['User-Agent']) {
-      headers['User-Agent'] = USER_AGENT;
-    } else if (!headers['User-Agent'].includes(`${PRODUCT_NAME}/`)) {
-      headers['User-Agent'] = `${headers['User-Agent']} ${USER_AGENT}`;
-    }
-
-    options.headers = headers;
-
-    return this.transporter.request<T>(options);
-  }
-
   /**
    * The main authentication interface. It takes an optional url which when
    * present is the endpoint being accessed, and returns a Promise which
@@ -303,6 +293,31 @@ export abstract class AuthClient
     return headers;
   }
 
+  static readonly DEFAULT_REQUEST_INTERCEPTOR: Parameters<
+    Gaxios['interceptors']['request']['add']
+  >[0] = {
+    resolved: async config => {
+      const headers = config.headers || {};
+
+      // Set `x-goog-api-client`, if not already set
+      if (!headers['x-goog-api-client']) {
+        const nodeVersion = process.version.replace(/^v/, '');
+        headers['x-goog-api-client'] = `gl-node/${nodeVersion}`;
+      }
+
+      // Set `User-Agent`
+      if (!headers['User-Agent']) {
+        headers['User-Agent'] = USER_AGENT;
+      } else if (!headers['User-Agent'].includes(`${PRODUCT_NAME}/`)) {
+        headers['User-Agent'] = `${headers['User-Agent']} ${USER_AGENT}`;
+      }
+
+      config.headers = headers;
+
+      return config;
+    },
+  };
+
   /**
    * Retry config for Auth-related requests.
    *
diff --git a/test/test.authclient.ts b/test/test.authclient.ts
index 2faa0f15..28261eed 100644
--- a/test/test.authclient.ts
+++ b/test/test.authclient.ts
@@ -16,6 +16,7 @@ import {strict as assert} from 'assert';
 
 import {PassThroughClient} from '../src';
 import {snakeToCamel} from '../src/util';
+import {Gaxios} from 'gaxios';
 
 describe('AuthClient', () => {
   it('should accept and normalize snake case options to camel case', () => {
@@ -38,4 +39,31 @@ describe('AuthClient', () => {
       assert.equal(authClient[camelCased], value);
     }
   });
+
+  it('should allow disabling of the default interceptor', () => {
+    const gaxios = new Gaxios();
+    const originalInterceptorCount = gaxios.interceptors.request.size;
+
+    const authClient = new PassThroughClient({
+      gaxios,
+      useAuthRequestParameters: false,
+    });
+
+    assert.equal(authClient.transporter, gaxios);
+    assert.equal(
+      authClient.transporter.interceptors.request.size,
+      originalInterceptorCount
+    );
+  });
+
+  it('should add the default interceptor exactly once between instances', () => {
+    const gaxios = new Gaxios();
+    const originalInterceptorCount = gaxios.interceptors.request.size;
+    const expectedInterceptorCount = originalInterceptorCount + 1;
+
+    new PassThroughClient({gaxios});
+    new PassThroughClient({gaxios});
+
+    assert.equal(gaxios.interceptors.request.size, expectedInterceptorCount);
+  });
 });