Explicitly rejecting empty hostname

This is not a breaking change, because the pre-existing implementation
will error out anyway, but with a less meaningful exception.

Author: rayluo

msal/authority.py

@@ -178,7 +178,7 @@ def user_realm_discovery(self, username, correlation_id=None, response=None):
 def canonicalize(authority_or_auth_endpoint):
     # Returns (url_parsed_result, hostname_in_lowercase, tenant)
     authority = urlparse(authority_or_auth_endpoint)
-    if authority.scheme == "https":
+    if authority.scheme == "https" and authority.hostname:
         parts = authority.path.split("/")
         first_part = parts[1] if len(parts) >= 2 and parts[1] else None
         if authority.hostname.endswith(_CIAM_DOMAIN_SUFFIX):  # CIAM
@@ -192,7 +192,7 @@ def canonicalize(authority_or_auth_endpoint):
             return authority, authority.hostname, parts[1]
     raise ValueError(
         "Your given address (%s) should consist of "
-        "an https url with a minimum of one segment in a path: e.g. "
+        "an https url with hostname and a minimum of one segment in a path: e.g. "
         "https://login.microsoftonline.com/{tenant} "
         "or https://{tenant_name}.ciamlogin.com/{tenant} "
         "or https://{tenant_name}.b2clogin.com/{tenant_name}.onmicrosoft.com/policy"

tests/test_authority.py

@@ -190,6 +190,10 @@ def test_canonicalize_rejects_tenantless_host_with_trailing_slash(self):
         with self.assertRaises(ValueError):
             canonicalize("https://no.tenant.example.com/")
 
+    def test_canonicalize_rejects_empty_host(self):
+        with self.assertRaises(ValueError):
+            canonicalize("https:///tenant")
+
 
 @unittest.skipIf(os.getenv("TRAVIS_TAG"), "Skip network io during tagged release")
 class TestAuthorityInternalHelperUserRealmDiscovery(unittest.TestCase):