test: Create external account integration tests for URL-based credent…

…ials (#726)

* Create external account integration tests for URL-based credentials

* rename byoid to external_account

* changes requested by bojeil@

system_tests/system_tests_sync/test_external_accounts.py

@@ -34,11 +34,14 @@
 
 import json
 import os
+import socket
 from tempfile import NamedTemporaryFile
+import threading
 
 import sys
 import google.auth
 from googleapiclient import discovery
+from six.moves import BaseHTTPServer
 from google.oauth2 import service_account
 import pytest
 from mock import patch
@@ -136,3 +139,75 @@ def test_file_based_external_account(
                 },
             },
         )
+
+
+# This test makes sure that setting up an http server to provide credentials
+# works to allow access to Google resources.
+def test_url_based_external_account(dns_access, oidc_credentials, service_account_info):
+    class TestResponseHandler(BaseHTTPServer.BaseHTTPRequestHandler):
+        def do_GET(self):
+            if self.headers["my-header"] != "expected-value":
+                self.send_response(400)
+                self.send_header("Content-Type", "application/json")
+                self.end_headers()
+                self.wfile.write(
+                    json.dumps({"error": "missing header"}).encode("utf-8")
+                )
+            elif self.path != "/token":
+                self.send_response(400)
+                self.send_header("Content-Type", "application/json")
+                self.end_headers()
+                self.wfile.write(
+                    json.dumps({"error": "incorrect token path"}).encode("utf-8")
+                )
+            else:
+                self.send_response(200)
+                self.send_header("Content-Type", "application/json")
+                self.end_headers()
+                self.wfile.write(
+                    json.dumps({"access_token": oidc_credentials.token}).encode("utf-8")
+                )
+
+    class TestHTTPServer(BaseHTTPServer.HTTPServer, object):
+        def __init__(self):
+            self.port = self._find_open_port()
+            super(TestHTTPServer, self).__init__(("", self.port), TestResponseHandler)
+
+        @staticmethod
+        def _find_open_port():
+            s = socket.socket()
+            s.bind(("", 0))
+            return s.getsockname()[1]
+
+        # This makes sure that the server gets shut down when this variable leaves its "with" block
+        # The python3 HttpServer has __enter__ and __exit__ methods, but python2 does not.
+        # By redefining the __enter__ and __exit__ methods, we ensure that python2 and python3 act similarly
+        def __exit__(self, *args):
+            self.shutdown()
+
+        def __enter__(self):
+            return self
+
+    with TestHTTPServer() as server:
+        threading.Thread(target=server.serve_forever).start()
+
+        assert get_project_dns(
+            dns_access,
+            {
+                "type": "external_account",
+                "audience": _AUDIENCE_OIDC,
+                "subject_token_type": "urn:ietf:params:oauth:token-type:jwt",
+                "token_url": "https://sts.googleapis.com/v1/token",
+                "service_account_impersonation_url": "https://iamcredentials.googleapis.com/v1/projects/-/serviceAccounts/{}:generateAccessToken".format(
+                    oidc_credentials.service_account_email
+                ),
+                "credential_source": {
+                    "url": "http://localhost:{}/token".format(server.port),
+                    "headers": {"my-header": "expected-value"},
+                    "format": {
+                        "type": "json",
+                        "subject_token_field_name": "access_token",
+                    },
+                },
+            },
+        )