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 Require Pushed Authorization Requests under Native Consoles > Access Management to enforce the use of the PAR endpoint to initiate authorization requests.

To force all clients in a realm to use PAR, configure the OAuth 2.0 provider’s advanced settings.

To force an individual client, go to Realms > Realm Name > Applications > OAuth 2.0 > Clients > Client ID and enable the setting on the Advanced tab.

The authorization code grant with PAR flow

Figure 1. OAuth 2.0 authorization code grant with PAR flow

The client pushes a request to the PAR endpoint, providing both client and request details.
Advanced Identity Cloud 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.
The client receives a request to access a protected resource. To access the resource, the client requires authorization from the resource owner.
The client redirects the resource owner’s user-agent to the authorization server.
The authorization server authenticates the resource owner, confirms resource access, and gathers consent if not previously saved.
The client requests an authorization code, typically through a web browser, by passing in the request_uri and client_id.
The client_id is validated against the request, and if successful, the authorization code is returned to the client.
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.
If the authorization code is valid, the authorization server returns an access token (and a refresh token, if configured) to the client.
The client requests access to the protected resources from the resource server.
The resource server contacts the authorization server to validate the access token.
The authorization server validates the token and responds to the resource server.
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:

Prepare the demonstration
Get a PAR request URI
Get an authorization code using REST or Get an authorization code using a browser
Exchange an authorization code for an access token

Prepare the demonstration

Complete these steps to prepare the authorization code grant with PAR flow demonstration:

Create an application owner profile and record the username and password.
Register a client application.
1. In the Advanced 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 Web.
3. Create the application, providing the following details:
  
  Name
  
  myClient
  
  Owners
  
  <application-owner>
  
  Client ID
  
  myClient
  
  Client Secret
  
  forgerock
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
5. Save your changes.
Configure the duration of the request URI:
1. Under Native Consoles > Access Management, go to Services > OAuth2 Provider and switch to the Advanced tab.
2. Set PAR Request URI Lifetime to a value sufficient to cover the duration of the PAR request.
  
  For more information, refer to PAR Request URI Lifetime.
3. Save your changes.
Create a resource owner profile and record the username and password.

Get a PAR request URI

As the client, call the authorization server’s PAR endpoint. Specify parameters directly in the request body. Alternatively, for large or sensitive data, Advanced Identity Cloud 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: myClient
client_secret: forgerock
request: <signed-encrypted-jwt-value>

Example parameters without a JWT:

client_id: myClient
client_secret: forgerock
redirect_uri: https://www.example.com:443/callback
scope: write
response_type: code
code_challenge: <code_challenge>
code_challenge_method: S256

For information about required parameters and an example JWT request object, refer to /oauth2/par.

Example PAR request with a JWT:

$ curl --request POST \
--data "client_id=myClient" \
--data "client_secret=forgerock" \
--data "request=<signed-encrypted-jwt-value>" \
"https://<tenant-env-fqdn>/am/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=<code_challenge>" \
--data "code_challenge_method=S256" \
--data "redirect_uri=https://www.example.com:443/callback" \
"https://<tenant-env-fqdn>/am/oauth2/realms/root/realms/alpha/par"

On success, the authorization server returns the following JSON:

{
  "request_uri": "zizBvZPwAmzfcDOMKTPv0QTaRA8",
  "expires_in": 90
}

request_uri: A reference to the PAR request payload.
expires_in: The validity period of the request URI in seconds.

Get an authorization code using a browser

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

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

client_id: myClient
response_type: code
redirect_uri: https://www.example.com:443/callback
request_uri: <par_request_uri>

For example:

https://<tenant-env-fqdn>/am/oauth2/realms/root/realms/alpha/authorize \
?client_id=myClient \
&request_uri=<par_request_uri>
&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.

The resource owner authenticates to the authorization server. In this demonstration, they sign in using the default journey configured for the realm.

By default, client applications in Advanced Identity Cloud use implied consent. If Advanced Identity Cloud is configured to require explicit consent, the authorization server presents the resource owner with a consent screen. To continue the flow, the resource owner must select Allow to grant consent.

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

Inspect the URL in the browser.

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

For example:

https://www.example.com/callback?code=<authorization-code>&iss...
Follow the steps to get an access token.

Get an authorization code using REST

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

Authenticate as the resource owner.

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"}

As the client, call the /oauth2/authorize endpoint to request the authorization code. Provide the resource owner’s SSO token in a cookie and the following parameters:

client_id: myClient
response_type: code
scope: write
request_uri: <par_request_uri>
csrf: <tokenId>
redirect_uri: https://www.example.com:443/callback
decision: allow

For information about the parameters supported by the /oauth2/authorize endpoint, refer to /oauth2/authorize.

For example:

$ curl --dump-header - \
--request POST \
--cookie "<session-cookie-name>=<tokenId>" \
--data "request_uri=<par_request_uri>" \
--data "client_id=myClient" \
--data "scope=write" \
--data "response_type=code" \
--data "csrf=<tokenId>" \
--data "redirect_uri=https://www.example.com:443/callback" \
--data "state=abc123" \
--data "decision=allow" \
"https://<tenant-env-fqdn>/am/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...
...

Perform the steps in Exchange an authorization code for an access token to get 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:

myClient:forgerock
grant_type: authorization_code
code: <authorization-code>
redirect_uri: https://www.example.com:443/callback

code_verifier: <code-verifier>

For example:

$ curl \
--request POST \
--user 'myClient:forgerock' \
--data "grant_type=authorization_code" \
--data "code=<authorization-code>" \
--data "redirect_uri=https://www.example.com:443/callback" \
--data "code_verifier=<code-verifier>" \
"https://<tenant-env-fqdn>/am/oauth2/realms/root/realms/alpha/access_token"

The redirect_uri and client 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, for example:

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

By default, the authorization server also issues a refresh token whenever it issues access tokens.

PingOne Advanced Identity Cloud

Authorization code grant with PAR

The authorization code grant with PAR flow

Demonstrate the authorization code grant with PAR flow

Prepare the demonstration

Get a PAR request URI

Get an authorization code using a browser

Get an authorization code using REST

Exchange an authorization code for an access token