QR Code Authentication

QR Code authentication is a strategy that allows the user to scan a QR code, generated by the CAS server, using a mobile device and subsequently login after having successfully validated it.

The QR code contains a special identifier embedded within that allows the mobile device to establish a communication channel using web sockets to the CAS server. Once established, the mobile device may collect credentials from the user and submit those to CAS for verification. The return result, expected as a JWT that is generated by CAS, is then passed along to the web socket channel for verification and successful login. Subsequent login attempts can allow for a completely passwordless scenario such that the mobile device can continue to re-use the JWT for authentication attempts, allowing the end user to scan and proceed.

Support is enabled by including the following dependency in the WAR overlay:

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<dependency>
  <groupId>org.apereo.cas</groupId>
  <artifactId>cas-server-support-qrlogin</artifactId>
  <version>${cas.version}</version>
</dependency>

Administrative Endpoints

The following endpoints are provided by CAS:

Configuration

To see the relevant list of CAS properties, please review this guide.

Web Socket Communication

The process of connecting to a web socket connection certainly varies for each mobile app framework. At a high level, mobile devices should establish a web socket connection to the CAS server via the /cas/qr-websocket endpoint. The payload must then be sent to the /qr/accept path as a map and must contain a token field that carries the pre-authenticated JWT. The payload header must point to the channel id obtained from the QR code under the header name QR_AUTHENTICATION_CHANNEL_ID as well as the authorized device identifier under QR_AUTHENTICATION_DEVICE_ID.

The following code snippet demonstrates this process as an example:

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let socket = new SockJS('https://sso.example.org/cas/qr-websocket');
let stompClient = Stomp.over(socket);
let payload = JSON.stringify({'token': '...'});   
let channelId = "...";      
let deviceId = "...";
stompClient.send("/qr/accept", 
    {'QR_AUTHENTICATION_CHANNEL_ID': channelId, 
     'QR_AUTHENTICATION_DEVICE_ID': deviceId}, 
    payload);

The following code snippet demonstrates this process for the Android platform based on StompProtocolAndroid:

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import ua.naiksoftware.stomp.*;
import ua.naiksoftware.stomp.dto.*;

String jwt = "...";
JSONStringer jsonWebToken = new JSONStringer().object()
  .key("token").value(jwt).endObject();

String channel = "...";      
String deviceId = "...";
List<StompHeader> headers = new ArrayList<>();
headers.add(new StompHeader("QR_AUTHENTICATION_CHANNEL_ID", channel));
headers.add(new StompHeader("QR_AUTHENTICATION_DEVICE_ID", deviceId));
headers.add(new StompHeader(StompHeader.DESTINATION, "/qr/accept"));

// wss://10.0.2.2 for ssl and localhost
StompClient client = Stomp.over(Stomp.ConnectionProvider.OKHTTP, 
  "wss://10.0.2.2:8443/cas/qr-websocket/websocket", null, httpClient);

client.connect();
StompMessage stompMessage = 
  new StompMessage(StompCommand.SEND, headers, jsonWebToken.toString());
client.send(stompMessage).subscribe();

Obtaining JWT

The mobile device should ask for and then submit user credentials to the CAS server using the REST protocol to obtain a JWT. The JWT request must also contain an additional request parameter QR_AUTHENTICATION_DEVICE_ID which indicates the authorized device identifier for the user.

Once the JWT is received, the device may cache the JWT and establish a session for code reuse later. The JWT should be sent to the CAS server’s web socket channel for validation and login as demonstrated above. The generated JWT is automatically signed and encrypted by CAS and can only be decoded by the CAS server.

Web Socket Channel

The QR code contains a special identifier embedded within that allows the mobile device to establish a communication channel using web sockets to the CAS server. The mobile device must be able to scan the QR code to extract the channel id in order to establish a communication route between CAS and the device.

Mobile Device Authorization

Registered devices are authorized and accepted by CAS using a dedicated QR device repository, that is able to track and link device identifiers to user ids. Such devices must be registered with CAS using an external registration mechanism or via available CAS-provided APIs.

By default, all devices can authenticate using the QR code. Different device repository implementations can be supplied using one of the strategies outlined below.

JSON

Authorized devices can be managed and tracked inside a single JSON resource, whose path is taught to CAS via settings. To see the relevant list of CAS properties, please review this guide.

Custom

Provide the appropriate bean implementation below to define a custom strategy for managing registered devices.

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@Bean
public QRAuthenticationDeviceRepository qrAuthenticationDeviceRepository() {
    return ...
}