diff --git a/packages/rules-unit-testing/src/api/index.ts b/packages/rules-unit-testing/src/api/index.ts
index 4a47f1491fd..51d16209187 100644
--- a/packages/rules-unit-testing/src/api/index.ts
+++ b/packages/rules-unit-testing/src/api/index.ts
@@ -27,6 +27,7 @@ import * as request from 'request';
 import { base64 } from '@firebase/util';
 import { setLogLevel, LogLevel } from '@firebase/logger';
 import { Component, ComponentType } from '@firebase/component';
+import { base64Encode } from '@firebase/util';
 
 const { firestore, database, storage } = firebase;
 export { firestore, database, storage };
@@ -157,6 +158,11 @@ export type FirebaseEmulatorOptions = {
   };
 };
 
+function trimmedBase64Encode(val: string): string {
+  // Use base64url encoding and remove padding in the end (dot characters).
+  return base64Encode(val).replace(/\./g, "");
+}
+
 function createUnsecuredJwt(token: TokenOptions, projectId?: string): string {
   // Unsecured JWTs use "none" as the algorithm.
   const header = {
@@ -198,12 +204,11 @@ function createUnsecuredJwt(token: TokenOptions, projectId?: string): string {
   // Unsecured JWTs use the empty string as a signature.
   const signature = '';
   return [
-    base64.encodeString(JSON.stringify(header), /*webSafe=*/ false),
-    base64.encodeString(JSON.stringify(payload), /*webSafe=*/ false),
+    trimmedBase64Encode(JSON.stringify(header)),
+    trimmedBase64Encode(JSON.stringify(payload)),
     signature
   ].join('.');
 }
-
 export function apps(): firebase.app.App[] {
   return firebase.apps;
 }