diff --git a/osmapi/http.py b/osmapi/http.py
index 9c2bd80..d368401 100644
--- a/osmapi/http.py
+++ b/osmapi/http.py
@@ -68,7 +68,8 @@ def _http_request(  # noqa: C901
         `return_value` indicates wheter this request should return
         any data or not.
 
-        If the username or password is missing,
+        If the username or password is missing
+        and no Authorization header is present,
         `OsmApi.UsernamePasswordMissingError` is raised.
 
         If the requested element has been deleted,
@@ -85,8 +86,10 @@ def _http_request(  # noqa: C901
         # Add API base URL to path
         path = self._api + path
 
-        if auth and not self._auth:
-            raise errors.UsernamePasswordMissingError("Username/Password missing")
+        if auth and not (self._auth or self._session.headers.get("Authorization")):
+            raise errors.UsernamePasswordMissingError(
+                "No username/password or 'Authorization' header provided"
+            )
 
         try:
             response = self._session.request(
diff --git a/tests/changeset_test.py b/tests/changeset_test.py
index 67125ad..1553781 100644
--- a/tests/changeset_test.py
+++ b/tests/changeset_test.py
@@ -505,7 +505,9 @@ def test_changeset_upload_no_auth(api):
 
     with pytest.raises(osmapi.UsernamePasswordMissingError) as execinfo:
         api.changeset_upload(changesdata)
-    assert str(execinfo.value) == "Username/Password missing"
+    assert (
+            str(execinfo.value) == "No username/password or 'Authorization' header provided"
+    )
 
 
 def test_changeset_download(api, add_response):
@@ -707,10 +709,33 @@ def test_changeset_comment(auth_api, add_response):
     }
 
 
+def test_changeset_comment_with_session_authorization_header(add_response):
+    resp = add_response(
+        POST,
+        "/changeset/123/comment",
+        filename="test_ChangesetComment.xml",
+    )
+    
+    session = requests.Session()
+    session.headers.update({"Authorization": "Bearer test-token"})
+    api = osmapi.OsmApi(api="http://api06.dev.openstreetmap.org", session=session)
+    
+    try:
+        result = api.ChangesetComment(123, comment="test comment")
+    finally:
+        api.close()
+    
+    assert len(resp.calls) == 1
+    assert resp.calls[0].request.body == "text=test+comment"
+    assert result["id"] == 123
+
+
 def test_changeset_comment_no_auth(api):
     with pytest.raises(osmapi.UsernamePasswordMissingError) as execinfo:
         api.changeset_comment(123, comment="test comment")
-    assert str(execinfo.value) == "Username/Password missing"
+    assert (
+            str(execinfo.value) == "No username/password or 'Authorization' header provided"
+    )
 
 
 def test_changeset_subscribe(auth_api, add_response):
@@ -763,7 +788,9 @@ def test_changeset_subscribe_when_already_subscribed(auth_api, add_response):
 def test_changeset_subscribe_no_auth(api):
     with pytest.raises(osmapi.UsernamePasswordMissingError) as execinfo:
         api.changeset_subscribe(45627)
-    assert str(execinfo.value) == "Username/Password missing"
+    assert (
+            str(execinfo.value) == "No username/password or 'Authorization' header provided"
+    )
 
 
 def test_changeset_unsubscribe(auth_api, add_response):
@@ -803,4 +830,6 @@ def test_changeset_unsubscribe_when_not_subscribed(auth_api, add_response):
 def test_changeset_unsubscribe_no_auth(api):
     with pytest.raises(osmapi.UsernamePasswordMissingError) as execinfo:
         api.changeset_unsubscribe(45627)
-    assert str(execinfo.value) == "Username/Password missing"
+    assert (
+            str(execinfo.value) == "No username/password or 'Authorization' header provided"
+    )
diff --git a/tests/node_test.py b/tests/node_test.py
index 8226ac0..d8f486b 100644
--- a/tests/node_test.py
+++ b/tests/node_test.py
@@ -120,7 +120,7 @@ def test_node_create_existing_node(self):
 
     def test_node_create_wo_auth(self):
         self._session_mock()
-
+        
         # setup mock
         self.api.changeset_create = mock.Mock(return_value=1111)
         self.api._current_changeset_id = 1111
@@ -131,7 +131,8 @@ def test_node_create_wo_auth(self):
         }
 
         with self.assertRaisesRegex(
-            osmapi.UsernamePasswordMissingError, "Username/Password missing"
+            osmapi.UsernamePasswordMissingError,
+            "No username/password or 'Authorization' header provided",
         ):
             self.api.node_create(test_node)
 
diff --git a/tests/osmapi_test.py b/tests/osmapi_test.py
index 0ff6bff..a4ffdc2 100644
--- a/tests/osmapi_test.py
+++ b/tests/osmapi_test.py
@@ -32,6 +32,7 @@ def _session_mock(self, auth=False, filenames=None, status=200):
         self.session_mock = mock.Mock()
         self.session_mock.request = mock.Mock(return_value=response_mock)
         self.session_mock.auth = None
+        self.session_mock.headers = {"Authorization": None}
 
         if auth:
             self.api = OsmApi(