Identity Cloud

Device authorization grant with PKCE

Endpoints

The device authorization grant is designed for client devices that have limited user interfaces, such as a set-top box. Since the devices are usually public clients and the device code can be intercepted by malicious users, you can combine the device flow with the Proof Key for Code Exchange (PKCE) standard (RFC 7636) to mitigate against interception attacks if the devices allow it.

Identity Cloud implements this grant by adding the following parameters to those used for the device authorization grant:

code_verifier

Contains a random string that correlates the authorization request to the token request.

code_challenge

Contains a string derived from the code verifier that is sent in the authorization request and needs to be verified later with the code verifier.

code_challenge_method

Contains the method used to derive the code challenge.

The device authorization grant flow with PKCE

OAuth 2.0 device authorization grant flow with PKCE
Figure 1. OAuth 2.0 device authorization grant flow with PKCE

  1. When using the PKCE standard, the device must be able to generate a code verifier and a code challenge. For details, refer to the PKCE standard (RFC 7636).

    For examples that generate a code verifier and a code challenge, refer to Generate a code verifier and a code challenge.

  2. The client device requests a device code from Identity Cloud, appending the code challenge previously generated to the request.

  3. Identity Cloud returns a device code, a user code, a URL for entering the user code, and an interval, in seconds.

  4. The client device provides instructions to the user to enter the user code. The client can choose an appropriate method to convey the instructions, for example, text instructions on screen, or a QR code.

  5. The client device begins to continuously poll Identity Cloud to check if authorization has been completed, appending the code verifier previously generated.

  6. If the user has not yet completed the authorization, Identity Cloud returns an HTTP 403 status code, with an authorization_pending message.

  7. The user follows the instructions from the client device to enter the user code by using a separate device.

  8. The authorization server verifies the code challenge stored in memory using the validation code. It also verifies the user code. If both codes are valid, Identity Cloud redirects the resource owner for authentication.

  9. Upon authentication, the user is prompted to confirm the user code. The page is pre-populated with the one entered before.

  10. The user can authorize the client device. The Identity Cloud consent page also displays the requested scopes, and their values.

    Identity Cloud does not display the confirmation nor the consent pages if the user has a valid session when they entered the code, and the client is allowed to skip consent.

    This is also true if you perform the call using REST and pass the decision=allow parameter.

  11. Upon authorization, Identity Cloud responds to the client device’s polling with an HTTP 200 status, and an access token, giving the client device access to the requested resources.

Demonstrate the device authorization grant flow with PKCE

Follow these steps to grant consent with a user code and poll for authorization:

Prepare the demonstration

Complete these steps to prepare the device authorization grant demonstration:

  1. Create an application owner profile and record the username and password.

  2. Register a client application.

    1. In the Identity Cloud admin UI, go to Applications and select + Custom Application.

    2. Select the sign-in method as OIDC - OpenId Connect and application type as Native / SPA.

    3. Create the application, providing the following details:

      Name

      myClient

      Owners

      <application-owner>

      Client ID

      myClient

    4. Switch to the Sign On tab and under General Settings, set these fields to have the following values:

      Sign-in URLs

      https://www.example.com:443/callback

      Scopes

      write

      Grant Types

      Device Code

      The Code Verifier Parameter Required setting in the AM admin UI (Realms > Realm Name > Services > OAuth2 Provider > Advanced) specifies whether Identity Cloud requires clients to include a code verifier in their calls.

      However, if a client makes a call to Identity Cloud with the code_challenge parameter, Identity Cloud honors the code exchange regardless of the value of Code Verifier Parameter Required. For more information, refer to Authorization server configuration.

    5. Save your changes.

  3. Create a resource owner profile and record the username and password.

Get a user code for the device

Devices can display a user code and instructions for a user. These can be used on a separate client to provide consent, allowing the device to access the resources.

Devices can display a user code and instructions for a user, which can be used on a separate client to provide consent, allowing the device to access resources.

User codes consist of a random selection of a configurable set of characters.

By default, the user code is generated using eight of the following characters:

234567ABCDEFGHIJKLMNOPQRSTVWXYZabcdefghijkmnopqrstvwxyz

You can configure the list of possible characters to improve usability. For example, remove similar characters such as 4 and A to reduce ambiguity on low resolution device screens, or limit input to either alphabetical or numerical characters to suit mobile keyboards.

The length of the user code is also configurable.

For more information, refer to the device flow configuration.

Perform the following steps to request a user code in the OAuth 2.0 device flow:

  1. As the client, call the /oauth2/device/code endpoint, specifying at least the following parameters:

    For information about client authentication methods, refer to Client application authentication.

    For example:

    $ curl \
--request POST \
--data "client_id=myClient" \
--data "code_challenge=<your-code-challenge>" \
--data "code_challenge_method=S256" \
--data "scope=write" \
"https://<tenant-env-fqdn>/am/oauth2/realms/root/realms/alpha/device/code"
{
    "interval": 5,
    "device_code": "7a95a0a4-6f13-42e3-ac3e-d3d159c94c55…​",
    "verification_uri": "https://<tenant-env-fqdn>/am/oauth2/realms/root/realms/alpha/device/user",
    "verification_url": "https://<tenant-env-fqdn>/am/oauth2/realms/root/realms/alpha/device/user",
    "verification_uri_complete": "https://<tenant-env-fqdn>/am/oauth2/realms/root/realms/alpha/device/user?user_code=VAL12e0v",
    "user_code": "VAL12e0v",
    "expires_in": 300
}

    On success, Identity Cloud returns a user code, a verification_uri, and a verification_uri_complete value comprising the user code appended to the URI, which can be used to create QR codes.

    The verification_url output is included to support earlier versions of the specification.

    Identity Cloud also returns an interval, in seconds, that the client device must wait for in between requests for an access token.

    In the Access Management console, go to Realms > Realm Name > Services > OAuth2 Provider > Device Flow to configure the returned values.

  2. The client device should now provide instructions to the user to enter the user code and grant access to the OAuth 2.0 device.

    The client may choose an appropriate method to convey the instructions, for example, text instructions on screen, or a QR code. Perform the steps in one of the following procedures:

  3. The client device should also begin polling the authorization server for the access token using the interval and device code information obtained in the previous step and the PKCE code verifier.

For more information, refer to Poll for authorization.

Grant consent using REST

The OAuth 2.0 device flow requires the user to grant consent to allow the client device to access the resources. The authorization server would then provide the client with an access token.

To grant consent with a user code without using a browser, perform the following steps:

  1. The resource owner logs in to the authorization server.

    For example:

    $ curl \
-i \
--request POST \
--header "Content-Type: application/json" \
--header "X-OpenAM-Username: <resource-owner-username>" \
--header "X-OpenAM-Password: <resource-owner-password>" \
--header "Accept-API-Version: resource=2.0, protocol=1.0" \
'https://<tenant-env-fqdn>/am/json/realms/root/realms/alpha/authenticate'
{"tokenId":"<tokenId>","successUrl":"/enduser/?realm=/alpha","realm":"/alpha"}

  2. As the client, call the /oauth2/device/user endpoint. Provide the resource owner’s SSO token in a cookie, and at least the following parameters:

    • user_code=<resource-owner-user-code>

    • decision=allow

    • csrf=<tokenId>

    For example:

    $ curl \
--request POST \
--header "Cookie: <session-cookie-name>=<tokenId>" \
--data "user_code=VAL12e0v" \
--data "decision=allow" \
--data "csrf=<tokenId>" \
"https://<tenant-env-fqdn>/am/oauth2/realms/root/realms/alpha/device/user"

    The scope and the client_id parameters are not required because the user code already contains that information.

    Identity Cloud returns HTML containing a JavaScript fragment named pageData, with details of the result.

    Successfully allowing or denying access returns:

    pageData = {
    locale: "en_US",
    baseUrl : "https://<tenant-env-fqdn>/am/XUI/",
    realm : "/alpha",
    done: true
}

    done: true means that the flow can now continue.

    If the supplied user code has already been used or is incorrect, Identity Cloud returns the following:

    pageData = {
    locale: "en_US",
    errorCode: "not_found",
    realm : "/alpha",
    baseUrl : "https://<tenant-env-fqdn>/am/XUI/"
    oauth2Data: {
          csrf: "ErFIk8pMraJ1rvKbloTgpp6b7GZ57kyk9HaIiKMVK3g=",
          userCode: "VAL12e0v",
    }
}

    As per Section 4.1.1 of the OAuth 2.0 authorization framework, it is required that the authorization server legitimately obtains an authorization decision from the resource owner.

    Any client using the endpoints to register consent is responsible for ensuring this requirement, Identity Cloud cannot assert that consent was given in these cases.

Grant consent using a browser

The OAuth 2.0 device flow requires that the user grants consent to allow the client device to access the resources.

The authorization server would then provide the client with an access token.

To grant consent with a user code using a browser, perform the following steps:

  1. The resource owner navigates to the verification URL acquired with the user code. For example:

    https://<tenant-env-fqdn>/am/oauth2/realms/root/realms/alpha/device/user

  2. The resource owner logs in to the authorization server.

  3. The resource owner enters their user code:

    Visit the verification URL to enter the user code.
    Figure 2. OAuth 2.0 User Code

    The verification_uri_complete property in the response appends the user code as a query parameter.

    Identity Cloud prefills the form with the user code value if provided in the user_code query parameter.

  4. The resource owner authorizes the device flow client by allowing the requested scopes:

    Identity Cloud lists the scopes requested by the client device, and their values.
    Figure 3. OAuth 2.0 Consent Page

    By default, client applications use implied consent. Identity Cloud does not display the screen to the user.

  5. Identity Cloud adds the OAuth 2.0 client to the user’s profile page in the Authorized Apps section and displays that the user is done with the flow:

    The user code part of the device flow is done.
    Figure 4. OAuth 2.0 Done Page

    The device that is polling the authorization server (Identity Cloud) can now obtain an access token.

Poll for authorization

The client device must poll the authorization server for an access token, since it cannot know whether the resource owner has already given consent or not.

Perform the following steps to poll for an access token:

  1. On the client device, create a POST request to poll the /oauth2/access_token endpoint to request an access token specifying, at least, the following parameters:

    • client_id=<your-client-id>

    • grant_type=urn:ietf:params:oauth:grant-type:device_code

    • device_code=<your-device-code>

    • code_verifier=<your-code-verifier>

    The client device must wait for the number of seconds previously provided as the value of interval between polling Identity Cloud for an access token. For example:

    $ curl \
--request POST \
--data "client_id=myClient" \
--data "grant_type=urn:ietf:params:oauth:grant-type:device_code" \
--data "device_code=<your-device-code>" \
--data "code_verifier=<your-code-verifier>" \
"https://<tenant-env-fqdn>/am/oauth2/realms/root/realms/alpha/access_token"

    If the user has authorized the client device, an HTTP 200 status code is returned, with an access token that can be used to request resources:

    {
    "access_token": "<access-token>",
    "refresh_token": "<refresh-token>",
    "scope": "write",
    "token_type": "Bearer",
    "expires_in": 3599
}

    If the user has not yet authorized the client device, an HTTP 403 status code is returned, with the following error message:

    {
    "error": "authorization_pending",
    "error_description": "The user has not yet completed authorization"
}

    If the client device is polling faster than the specified interval, an HTTP 400 status code is returned, with the following error message:

    {
    "error": "slow_down",
    "error_description": "The polling interval has not elapsed since the last request"
}
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