diff --git a/flask_oidc/__init__.py b/flask_oidc/__init__.py
index 1162f7e..b22a042 100644
--- a/flask_oidc/__init__.py
+++ b/flask_oidc/__init__.py
@@ -307,15 +307,34 @@ def require_login(self, view_func):
         @wraps(view_func)
         def decorated(*args, **kwargs):
             if not self.user_loggedin:
-                redirect_uri = "{login}?next={here}".format(
-                    login=url_for("oidc_auth.login"),
-                    here=quote_plus(request.url),
-                )
-                return redirect(redirect_uri)
+                return self.redirect_to_auth_server()
             return view_func(*args, **kwargs)
 
         return decorated
 
+    def redirect_to_auth_server(self, destination=None, customstate=None):
+        """
+        Redirect to the IdP.
+
+        :param destination: The page that the user was going to,
+            before we noticed they weren't logged in.
+        :type destination: Url to return the client to if a custom handler is
+            not used. Not available with custom callback.
+        :param customstate: Ignored, left here for compatibility.
+        :returns: A redirect response to start the login process.
+        """
+        if customstate is not None:
+            warnings.warn(
+                "The customstate argument of redirect_to_auth_server is ignored.",
+                DeprecationWarning,
+                stacklevel=2,
+            )
+        redirect_uri = "{login}?next={here}".format(
+            login=url_for("oidc_auth.login"),
+            here=quote_plus(destination or request.url),
+        )
+        return redirect(redirect_uri)
+
     def logout(self, return_to=None):
         """
         Request the browser to please forget the cookie we set, to clear the
diff --git a/tests/test_flask_oidc.py b/tests/test_flask_oidc.py
index 369c0d0..84e1118 100644
--- a/tests/test_flask_oidc.py
+++ b/tests/test_flask_oidc.py
@@ -176,6 +176,14 @@ def test_bad_token(client):
     assert "Internal Server Error" in resp.get_data(as_text=True)
 
 
+def test_redirect_obsolete_argument(test_app):
+    with test_app.test_request_context(path="/somewhere"):
+        with pytest.warns(DeprecationWarning):
+            resp = test_app.oidc_ext.redirect_to_auth_server(None, "dummy")
+    assert resp.status_code == 302
+    assert resp.location == "/login?next=http%3A%2F%2Flocalhost%2Fsomewhere"
+
+
 def test_user_getinfo(test_app, client, dummy_token):
     user_info = {"nickname": "dummy"}
     with test_app.test_request_context(path="/somewhere"):