Fix firebase test

Change-Id: I9eafee2e80a640ee3407a6ff22f9e1125e510100

Author: Jon Wayne Parrott

appengine/standard/firebase/firenotes/backend/firebase_helper.py

@@ -112,8 +112,8 @@ def verify_auth_token(request):
             public_key,
             algorithms=['RS256'],
             audience=os.environ['FIREBASE_PROJECT_ID'],
-            issuer="https://securetoken.google.com/"
-            + os.environ['FIREBASE_PROJECT_ID'])
+            issuer='https://securetoken.google.com/{}'.format(
+                os.environ['FIREBASE_PROJECT_ID']))
     except jwt.exceptions.InvalidTokenError as e:
         logging.warning('JWT verification failed: {}'.format(e))
         return None

appengine/standard/firebase/firenotes/backend/firebase_helper_test.py

@@ -94,7 +94,7 @@ def test_extract_public_key_from_certificate(test_certificate):
 
 def make_jwt(private_key_bytes, claims=None, headers=None):
     jwt_claims = {
-        'iss': 'http://example.com',
+        'iss': 'https://securetoken.google.com/test_audience',
         'aud': 'test_audience',
         'user_id': '123',
         'sub': '123',