diff --git a/.gitignore b/.gitignore
index f01e60e..6d86d1f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -41,6 +41,3 @@
 pytype_output/
 
 .python-version
-.DS_Store
-cert_path
-key_path
\ No newline at end of file
diff --git a/google/auth/iam.py b/google/auth/iam.py
index 9e38879..bd05004 100644
--- a/google/auth/iam.py
+++ b/google/auth/iam.py
@@ -28,7 +28,7 @@
 from google.auth import crypt
 from google.auth import exceptions
 
-_IAM_API_ROOT_URI = "https://iamcredentials.googleapis.com/v1"
+_IAM_API_ROOT_URI = "https://iam.googleapis.com/v1"
 _SIGN_BLOB_URI = _IAM_API_ROOT_URI + "/projects/-/serviceAccounts/{}:signBlob?alt=json"
 
 
@@ -71,7 +71,7 @@
         url = _SIGN_BLOB_URI.format(self._service_account_email)
         headers = {}
         body = json.dumps(
-            {"payload": base64.b64encode(message).decode("utf-8")}
+            {"bytesToSign": base64.b64encode(message).decode("utf-8")}
         ).encode("utf-8")
 
         self._credentials.before_request(self._request, method, url, headers)
@@ -97,4 +97,4 @@
     @_helpers.copy_docstring(crypt.Signer)
     def sign(self, message):
         response = self._make_signing_request(message)
-        return base64.b64decode(response["signedBlob"])
+        return base64.b64decode(response["signature"])
diff --git a/system_tests/test_service_account.py b/system_tests/test_service_account.py
index 498b75b..262ce84 100644
--- a/system_tests/test_service_account.py
+++ b/system_tests/test_service_account.py
@@ -16,7 +16,6 @@
 
 from google.auth import _helpers
 from google.auth import exceptions
-from google.auth import iam
 from google.oauth2 import service_account
 
 
@@ -47,19 +46,3 @@
             "https://www.googleapis.com/auth/userinfo.profile",
         ]
     )
-
-def test_iam_signer(http_request, credentials):
-    credentials = credentials.with_scopes(
-        ["https://www.googleapis.com/auth/iam"]
-    )
-
-    # Verify iamcredentials signer.
-    signer = iam.Signer(
-        http_request,
-        credentials,
-        credentials.service_account_email
-    )
-    
-    signed_blob = signer.sign("message")
-
-    assert isinstance(signed_blob, bytes)
diff --git a/tests/compute_engine/test_credentials.py b/tests/compute_engine/test_credentials.py
index 4ee6536..8c95e24 100644
--- a/tests/compute_engine/test_credentials.py
+++ b/tests/compute_engine/test_credentials.py
@@ -363,11 +363,11 @@
         signature = base64.b64encode(b"some-signature").decode("utf-8")
         responses.add(
             responses.POST,
-            "https://iamcredentials.googleapis.com/v1/projects/-/"
-            "serviceAccounts/service-account@example.com:signBlob?alt=json",
+            "https://iam.googleapis.com/v1/projects/-/serviceAccounts/"
+            "service-account@example.com:signBlob?alt=json",
             status=200,
             content_type="application/json",
-            json={"keyId": "some-key-id", "signedBlob": signature},
+            json={"keyId": "some-key-id", "signature": signature},
         )
 
         id_token = "{}.{}.{}".format(
@@ -477,11 +477,11 @@
         signature = base64.b64encode(b"some-signature").decode("utf-8")
         responses.add(
             responses.POST,
-            "https://iamcredentials.googleapis.com/v1/projects/-/"
-            "serviceAccounts/service-account@example.com:signBlob?alt=json",
+            "https://iam.googleapis.com/v1/projects/-/serviceAccounts/"
+            "service-account@example.com:signBlob?alt=json",
             status=200,
             content_type="application/json",
-            json={"keyId": "some-key-id", "signedBlob": signature},
+            json={"keyId": "some-key-id", "signature": signature},
         )
 
         id_token = "{}.{}.{}".format(
diff --git a/tests/test_iam.py b/tests/test_iam.py
index e20eeba..4367fe7 100644
--- a/tests/test_iam.py
+++ b/tests/test_iam.py
@@ -81,7 +81,7 @@
     def test_sign_bytes(self):
         signature = b"DEADBEEF"
         encoded_signature = base64.b64encode(signature).decode("utf-8")
-        request = make_request(http_client.OK, data={"signedBlob": encoded_signature})
+        request = make_request(http_client.OK, data={"signature": encoded_signature})
         credentials = make_credentials()
 
         signer = iam.Signer(request, credentials, mock.sentinel.service_account_email)