diff --git a/caldav/davclient.py b/caldav/davclient.py
index b9325e7..ce9183a 100644
--- a/caldav/davclient.py
+++ b/caldav/davclient.py
@@ -616,11 +616,9 @@ def delete(self, url: str) -> DAVResponse:
     def options(self, url: str) -> DAVResponse:
         return self.request(url, "OPTIONS")
 
-    def extract_auth_types(self, header):
-        auth_types = header.lower().split(",")
-        auth_types = map(lambda auth_type: auth_type.strip(), auth_types)
-        auth_types = map(lambda auth_type: auth_type.split(" ")[0], auth_types)
-        return list(filter(lambda auth_type: auth_type, auth_types))
+    def extract_auth_types(self, header: str):
+        # https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/WWW-Authenticate#syntax
+        return {h.split()[0] for h in header.lower().split(",")}
 
     def request(
         self,
diff --git a/tests/test_caldav_unit.py b/tests/test_caldav_unit.py
index a4486be..9321294 100644
--- a/tests/test_caldav_unit.py
+++ b/tests/test_caldav_unit.py
@@ -1293,12 +1293,12 @@ def testExtractAuth(self):
         """
         cal_url = "http://me:hunter2@calendar.example:80/"
         with DAVClient(url=cal_url) as client:
-            assert client.extract_auth_types("Basic\n") == ["basic"]
-            assert client.extract_auth_types("Basic") == ["basic"]
-            assert client.extract_auth_types('Basic Realm=foo;charset="UTF-8"') == [
+            assert client.extract_auth_types("Basic\n") == {"basic"}
+            assert client.extract_auth_types("Basic") == {"basic"}
+            assert client.extract_auth_types('Basic Realm=foo;charset="UTF-8"') == {
                 "basic"
-            ]
-            assert client.extract_auth_types("Basic,dIGEST Realm=foo") == [
+            }
+            assert client.extract_auth_types("Basic,dIGEST Realm=foo") == {
                 "basic",
                 "digest",
-            ]
+            }