diff --git a/litellm/proxy/management_endpoints/ui_sso.py b/litellm/proxy/management_endpoints/ui_sso.py
index 5e6aabd70ac..39e015f3928 100644
--- a/litellm/proxy/management_endpoints/ui_sso.py
+++ b/litellm/proxy/management_endpoints/ui_sso.py
@@ -1791,11 +1791,7 @@ class SSOAuthenticationHandler:
                 detail="return_to is not allowed: control_plane_url is not configured",
             )
 
-        parsed_cp = urlparse(control_plane_url)
-        parsed_return = urlparse(return_to)
-        cp_origin = f"{parsed_cp.scheme}://{parsed_cp.netloc}"
-        return_origin = f"{parsed_return.scheme}://{parsed_return.netloc}"
-        if cp_origin != return_origin:
+        if urlparse(return_to).hostname != urlparse(control_plane_url).hostname:
             raise HTTPException(
                 status_code=400,
                 detail="return_to does not match the configured control_plane_url",
diff --git a/litellm/proxy/proxy_server.py b/litellm/proxy/proxy_server.py
index 48d9d18fe46..73b224d4bba 100644
--- a/litellm/proxy/proxy_server.py
+++ b/litellm/proxy/proxy_server.py
@@ -11080,6 +11080,14 @@ async def login_v3(request: Request):  # noqa: PLR0915
     from litellm.proxy.utils import get_custom_url
 
     try:
+        if not general_settings.get("control_plane_url"):
+            raise ProxyException(
+                message="/v3/login is only available on workers with control_plane_url configured",
+                type=ProxyErrorTypes.not_found_error,
+                param="control_plane_url",
+                code=status.HTTP_404_NOT_FOUND,
+            )
+
         body = await request.json()
         username = str(body.get("username"))
         password = str(body.get("password"))
diff --git a/tests/test_litellm/proxy/management_endpoints/test_ui_sso.py b/tests/test_litellm/proxy/management_endpoints/test_ui_sso.py
index d48dcc52f59..4d531da67ca 100644
--- a/tests/test_litellm/proxy/management_endpoints/test_ui_sso.py
+++ b/tests/test_litellm/proxy/management_endpoints/test_ui_sso.py
@@ -5211,3 +5211,12 @@ class TestValidateReturnTo:
             SSOAuthenticationHandler._validate_return_to("https://evil.com/phish")
         assert exc_info.value.status_code == 400
 
+    def test_case_insensitive_hostname(self, monkeypatch):
+        """Hostname comparison should be case-insensitive per RFC 3986."""
+        monkeypatch.setattr(
+            "litellm.proxy.proxy_server.general_settings",
+            {"control_plane_url": "https://CP.Example.COM"},
+        )
+        # Should not raise
+        SSOAuthenticationHandler._validate_return_to("https://cp.example.com/ui")
+
diff --git a/tests/test_litellm/proxy/test_proxy_server.py b/tests/test_litellm/proxy/test_proxy_server.py
index e6269936b5c..f23f5a39353 100644
--- a/tests/test_litellm/proxy/test_proxy_server.py
+++ b/tests/test_litellm/proxy/test_proxy_server.py
@@ -236,8 +236,25 @@ def test_login_v2_returns_json_on_invalid_json_body(monkeypatch):
     assert isinstance(data["error"], dict)
 
 
-def test_login_v3_always_includes_token_in_body(monkeypatch):
-    """v3/login always returns token in body, even without worker_registry."""
+def test_login_v3_rejected_without_control_plane_url(monkeypatch):
+    """v3/login returns 404 when control_plane_url is not configured."""
+    mock_prisma_client = MagicMock()
+    monkeypatch.setattr("litellm.proxy.proxy_server.master_key", "test-master-key")
+    monkeypatch.setattr("litellm.proxy.proxy_server.general_settings", {})
+    monkeypatch.setattr("litellm.proxy.proxy_server.prisma_client", mock_prisma_client)
+
+    client = TestClient(app)
+    response = client.post(
+        "/v3/login",
+        json={"username": "alice", "password": "secret"},
+    )
+
+    assert response.status_code == 404
+    assert "control_plane_url" in response.json()["error"]["message"]
+
+
+def test_login_v3_includes_token_in_body(monkeypatch):
+    """v3/login returns token in body when control_plane_url is configured."""
     mock_prisma_client = MagicMock()
     monkeypatch.setattr(
         "litellm.proxy.auth.login_utils.authenticate_user",
@@ -249,7 +266,10 @@ def test_login_v3_always_includes_token_in_body(monkeypatch):
     )
     monkeypatch.setattr("jwt.encode", MagicMock(return_value="signed-token"))
     monkeypatch.setattr("litellm.proxy.proxy_server.master_key", "test-master-key")
-    monkeypatch.setattr("litellm.proxy.proxy_server.general_settings", {})
+    monkeypatch.setattr(
+        "litellm.proxy.proxy_server.general_settings",
+        {"control_plane_url": "https://cp.example.com"},
+    )
     monkeypatch.setattr("litellm.proxy.proxy_server.premium_user", False)
     monkeypatch.setattr("litellm.proxy.proxy_server.prisma_client", mock_prisma_client)
     mock_config = MagicMock()
@@ -289,6 +309,10 @@ def test_login_v3_returns_json_on_proxy_exception(monkeypatch):
         mock_authenticate_user,
     )
     monkeypatch.setattr("litellm.proxy.proxy_server.master_key", "test-master-key")
+    monkeypatch.setattr(
+        "litellm.proxy.proxy_server.general_settings",
+        {"control_plane_url": "https://cp.example.com"},
+    )
     monkeypatch.setattr("litellm.proxy.proxy_server.prisma_client", mock_prisma_client)
 
     client = TestClient(app)