Use buffer.toString directly on the provided string to address PR feedback.

Author: macastelaz

core/packages/google-auth-library-nodejs/src/auth/gdchclient.ts

@@ -297,10 +297,6 @@ export class GdchClient extends OAuth2Client {
 
   private base64UrlEncode(str: string | Buffer): string {
     const buffer = typeof str === 'string' ? Buffer.from(str) : str;
-    return buffer
-      .toString('base64')
-      .replace(/=/g, '')
-      .replace(/\+/g, '-')
-      .replace(/\//g, '_');
+    return buffer.toString('base64url');
   }
 }

core/packages/google-auth-library-nodejs/test/test.gdchclient.ts

@@ -484,4 +484,24 @@ describe('GdchClient', () => {
     });
     scope.done();
   });
+
+  describe('base64UrlEncode', () => {
+    it('should correctly encode strings and buffers in base64url format', () => {
+      const client = new GdchClient();
+      const testCases = [
+        {input: 'hello world', expected: 'aGVsbG8gd29ybGQ'},
+        {input: 'foo bar baz', expected: 'Zm9vIGJhciBiYXo'},
+        {input: 'this is a test', expected: 'dGhpcyBpcyBhIHRlc3Q'},
+        {input: 'n>?', expected: 'bj4_'},
+        {input: 'n>~', expected: 'bj5-'},
+      ];
+
+      for (const tc of testCases) {
+        const stringResult = (client as any).base64UrlEncode(tc.input);
+        const bufferResult = (client as any).base64UrlEncode(Buffer.from(tc.input));
+        assert.strictEqual(stringResult, tc.expected);
+        assert.strictEqual(bufferResult, tc.expected);
+      }
+    });
+  });
 });