Access Management 7.3.2

Authorization code grant with PAR

Endpoints

The pushed authorization request (PAR) endpoint provides enhanced security and cryptographic integrity when used with the authorization code grant flow, and optionally, in conjunction with PKCE.

PAR lets the authorization server authenticate the client before making an authorization request to enable early detection of invalid or illegal requests.

To further protect authorization details when passing through third-party applications, clients can use JWT-based request objects as defined by RFC9101, to wrap confidential and potentially complex request parameters.

In response to this pre-authorization backchannel request, the client receives a request URI that is used to reference the payload data in subsequent interactions with the server.

PAR is optional by default, but you can enable the Require Pushed Authorization Requests setting in the AM admin UI to enforce the use of the PAR endpoint to initiate authorization requests.

To force all clients to use PAR, configure the OAuth 2.0 provider advanced settings. To force an individual client, configure the client settings.

The authorization code grant with PAR flow

OAuth 2.0 authorization code grant flow
Figure 1. OAuth 2.0 authorization code grant flow

  1. The client pushes a request to the PAR endpoint, providing both client and request details.

  2. AM validates both client and request, and if successful, returns a request URI as a reference to the request payload and an expiry period for the request URI.

  3. The client receives a request to access a protected resource. To access the resources, the client requires authorization from the resource owner.

  4. The client redirects the resource owner’s user-agent to the authorization server.

  5. The authorization server authenticates the resource owner, confirms resource access, and gathers consent if not previously saved.

  6. The client requests an authorization code, typically through a web browser, by passing in the request_uri and client_id.

  7. The client_id is validated against the request, and if successful, the authorization code is returned to the client.

  8. The client authenticates to the authorization server using the received code in exchange for an access token.

    Note that this example assumes a confidential client. Public clients are not required to authenticate.

  9. If the authorization code is valid, the authorization server returns an access token (and a refresh token, if configured) to the client.

  10. The client requests access to the protected resources from the resource server.

  11. The resource server contacts the authorization server to validate the access token.

  12. The authorization server validates the token and responds to the resource server.

  13. If the token is valid, the resource server allows the client to access the protected resource.

Demonstrate the authorization code grant with PAR flow

Perform these steps to get a PAR request URI and an authorization code to exchange for an access token:

  1. Prepare the demonstration

  2. Get a PAR request URI

  3. Get an authorization code using REST or Get an authorization code using a browser

  4. Exchange an authorization code for an access token

Prepare the demonstration

This demonstration assumes the following configuration:

  • AM is configured as an OAuth 2.0 authorization server. Ensure that:

    • The code plugin is configured in the Response Type Plugins field.

    • The Authorization Code grant type is configured in the Grant Types field.

    • The PAR Request URI Lifetime attribute is set to a value sufficient to cover the duration of the PAR request.

    For more information, refer to Authorization server configuration.

  • A confidential client called myClient is registered in AM with the following configuration:

    • Client secret: forgerock

    • Scopes: write

    • Response Types: code

    • Grant Types: Authorization Code

    For more information, refer to Client application registration. Complete these steps to prepare the authorization code grant with PAR flow demonstration:

Get a PAR request URI

As the client, call the authorization server’s /oauth2/par endpoint. Specify parameters directly in the request body. Alternatively, for large or sensitive data, AM supports the JWT-Secured Authorization Request (JAR) standard for PAR, which lets you wrap parameters in a signed and encrypted JWT.

Example parameters with a JWT:

  • client_id=your-client-id

  • client_secret=your-client-secret

  • request=signed-encrypted-JWT-value

Example parameters without a JWT:

  • client_id=your-client-id

  • client_secret=your-client-secret

  • redirect_uri=your-redirect-id

  • scope=write

  • response_type=code,

  • code_challenge=QR1D-7w1-rOQvlFe1CeqZigqaIpmZXatDMVvZ50o

  • code_challenge_method=S256

Example PAR request with a JWT:

$ curl \
--request POST \
--data "client_id=myClient" \
--data "client_secret=forgerock" \
--data "request=eyJhbGciOiJIUzI1NiJ…​mnRTwgPGTqkp5UBTVWaA_CifxWx1ikcZofOas" \
"https://openam.example.com:8443/openam/oauth2/realms/root/realms/alpha/par"

Example PAR request without a JWT:

$ curl \
--request POST \
--data "client_id=myClient" \
--data "client_secret=forgerock" \
--data "response_type=code" \
--data "scope=write" \
--data "code_challenge=QR1D-7w1-rOQvlFe1CeqZigqaIpmZXatDMVvZ50o" \
--data "code_challenge_method=S256" \
--data "redirect_uri=https://www.example.com:443" \
"https://openam.example.com:8443/openam/oauth2/realms/root/realms/alpha/par"

On success, AM returns the following JSON:

{
  "request_uri": "C2c3yhu2IApAELttmZtfPNPQaIJxvTCHk", (1)
  "expires_in": 90 (2)
}
1 request_uri: A reference to the PAR request payload.
2 expires_in: The validity period of the request URI in seconds.

Get an authorization code using a browser

  1. Ensure the client has retrieved a request URI by following the steps described in Get a PAR request URI.

  2. The client redirects the resource owner’s user-agent to the authorization server’s /oauth2/authorize endpoint, including the following parameters:

    • client_id=your-client-id

    • response_type=code

    • redirect_uri=your-redirect-id

    • request_uri=the-PAR-request-uri

    For example:

    https://openam.example.com:8443/openam/oauth2/realms/root/realms/alpha/authorize \
?client_id=myClient \
&request_uri=C2c3yhu2IApAELttmZtfPNPQaIJxvTCHk
&response_type=code \
&scope=write \
&state=abc123 \
&redirect_uri=https://www.example.com:443/callback

    The URL is split and spaces added for readability purposes.

    The scope parameter is optional if default values are configured in the authorization server or the client.

    The state parameter is included to protect against CSRF attacks but is also optional.

  3. The resource owner authenticates to the authorization server, for example, using the credentials of the demo user. In this case, they log in using the default chain or tree configured for the realm.

  4. On a successful login, the authorization server presents the AM consent screen unless AM is configured to use implied consent.

    The OAuth 2.0 AM user interface consent screen requesting access to the write scope.
    Figure 2. OAuth 2.0 consent screen

  5. Click Allow to consent.

    The authorization server redirects the resource owner to the URL specified in the redirect_uri parameter.

  6. Inspect the URL in the browser.

    It contains a code parameter with the authorization code the authorization server has issued.

    For example:

    http://www.example.com/callback?code=g5B3qZ8rWzKIU2xodV_kkSIk0F4&scope=write&iss…​

  7. The client performs the steps in Exchange an authorization code for an access token to exchange the authorization code for an access token.

Get an authorization code using REST

  1. Ensure the client has retrieved a request URI by following the steps described in Get a PAR request URI.

  2. The resource owner logs in to the authorization server, for example, using the credentials of the demo user.

    For example:

    $ curl \
--request POST \
--header "Content-Type: application/json" \
--header "X-OpenAM-Username: demo" \
--header "X-OpenAM-Password: Ch4ng31t" \
--header "Accept-API-Version: resource=2.0, protocol=1.0" \
'https://openam.example.com:8443/openam/json/realms/root/realms/alpha/authenticate'
{
    "tokenId":"AQIC5wM…​TU3OQ*",
    "successUrl":"/openam/console",
    "realm":"/alpha"
}

  3. The client makes a POST call to the authorization server’s /oauth2/authorize endpoint, specifying the SSO token of the demo in a cookie and, at least, the following parameters:

    • client_id=your-client-id

    • request_uri=the-PAR-request-uri

    • response_type=code

    • redirect_uri=your-redirect-uri

    • decision=allow

    • csrf=demo-user-SSO-token

    For example:

    $ curl --dump-header - \
--request POST \
--Cookie "iPlanetDirectoryPro=AQIC5wM…​TU3OQ*" \
--data "request_uri=C2c3yhu2IApAELttmZtfPNPQaIJxvTCHk" \
--data "client_id=myClient" \
--data "scope=write" \
--data "response_type=code" \
--data "csrf=AQIC5wM…​TU3OQ*" \
--data "redirect_uri=https://www.example.com:443/callback" \
--data "state=abc123" \
--data "decision=allow" \
"https://openam.example.com:8443/openam/oauth2/realms/root/realms/alpha/authorize"

    The scope parameter is optional if default values are configured in the authorization server or the client.

    The state parameter is included to protect against CSRF attacks but is also optional.

    If the authorization server is able to authenticate the user and the client, it returns an HTTP 302 response with the authorization code appended to the redirection URL:

    HTTP/2 302
…​
location: https://www.example.com:443/callback?code=<authorization-code>&iss…​
…​

  4. Perform the steps in Exchange an authorization code for an access token to exchange the authorization code for an access token.

Exchange an authorization code for an access token

As the client, call the /oauth2/access_token endpoint to exchange the authorization code for an access token. Provide the following parameters:

  • grant_type=authorization_code

  • code=your-authorization-code

  • redirect_uri=your-redirect-uri

  • code_verifier=your-code-verifier

Confidential clients can authenticate to the OAuth 2.0 endpoints in several ways. This example uses the following form parameters:

  • client_id=your-client-id

  • client_secret=your-client-secret

For more information, refer to OAuth 2.0 client authentication.

For example:

$ curl \
--request POST \
--data "grant_type=authorization_code" \
--data "code=g5B3qZ8rWzKIU2xodV_kkSIk0F4" \
--data "client_id=myClient" \
--data "client_secret=forgerock" \
--data "redirect_uri=https://www.example.com:443/callback" \
--data "code_verifier=082b7ab3042995bcb3163ec8…​" \
"https://openam.example.com:8443/openam/oauth2/realms/root/realms/alpha/access_token"

The client_id and redirect_uri parameters specified in this call must match those used as part of the authorization code request, or the authorization server will not validate the code.

The authorization server returns an access token in the access_token property. For example:

{
  "access_token": "sbQZuveFumUDV5R1vVBl6QAGNB8",
  "scope": "write",
  "token_type": "Bearer",
  "expires_in": 3599
}

The authorization server can also issue refresh tokens at the same time the access tokens are issued. For more information, refer to Refresh tokens.