Client-Initiated Backchannel Authentication (CIBA) is an specification that allows a client application to initiate an authentication and/or without requiring direct user interaction on the initiating application. Rich Authorization Requests (RAR) is an OAuth 2.0 extension that allows client applications to request for more complex permissions beyond standard OAuth 2.0 scopes in an authorization request. You can use CIBA with RAR to pass data to the in a backchannel request. The authorization_details parameter contains details about the request that you can customize in a consent prompt to show the user.

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Common use cases

Use RAR with the CIBA flow for use cases that require more fine-grained control over resource access. Common use cases include:
  1. A payments app prompts the user to confirm a money transfer. The authorization_details can be customized to show the transaction details.
  2. An AI agent prompts the user with details about a rescheduled doctor’s appointment. The authorization_details can be customized to show the new time and date.

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How it works

The User Authorization with CIBA flow is similar to the User Authentication with CIBA flow, where RAR support enables clients to pass the authorization_details to the authorization server via the /bc-authorize endpoint. The following sequence diagram explains the end-to-end User Authorization with CIBA flow:
The sequence diagram defines two actors: an authorizing user and an initiating user. The authorizing and initiating user can be two different entities, such as an AI agent performing a task on a user’s behalf. In other use cases, they can be the same entity, such as a user authorizing a transaction on a retail kiosk or another connected device.

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Prerequisites

To initiate a CIBA push request using Auth0, you must complete the following prerequisites:
If you have set as always required for your tenant, users are prompted to enroll for MFA at their next login. You can also use Actions to prompt for MFA enrollment.

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Step 1: Client application initiates a CIBA request

Use the User Search APIs to find the authorizing user for whom you’d like to initiate a CIBA request and obtain their user ID. Once you have a user ID for the authorizing user, use the Authentication API to send a CIBA request with the authorization_details to the /bc-authorize endpoint: 
curl --location 'https://$tenant/bc-authorize' \
  --request POST \
  --header 'Content-Type: application/x-www-form-urlencoded' \
  --data-urlencode 'client_id=$client_id' \
  --data-urlencode 'client_secret=$client_secret' \
  --data-urlencode 'login_hint={ "format": "iss_sub", "iss": "https://$tenant/", "sub":"$user_id"}' \
  --data-urlencode 'audience=https://api.example.com' \
  --data-urlencode 'binding_message=Confirm payment of 2500' \
  --data-urlencode 'authorization_details=[{
      "type": "money_transfer", 
      "instructedAmount": {
        "amount": 2500, 
        "currency": "USD"
      }, 
      "sourceAccount": "xxxxxxxxxxx1234", 
      "destinationAccount": "xxxxxxxxxxx9876", 
      "beneficiary": "Hanna Herwitz", 
      "subject": "A Lannister Always Pays His Debts"
    }]'
ParametersDescription
tenantTenant name. It can also be a custom domain.
client_idClient application identifier.
client_secretClient authentication method used for user authentication with CIBA, such as Client Secret, Private Key JWT, or mTLS Authentication. If you’re using Private Key JWT or mTLS, you don’t need to include the client secret.
scopeIf the client needs to identify the user (i.e., obtain an id_token), openid must be included. If the client only needs an access token for authorization, openid is optional, but commonly included. The scope can optionally include offline_access to request a refresh token. However, for one-time authorization of a transaction with the CIBA Flow, a refresh token is not needed and does not have any meaning in this context.
user_idUser ID for the authorizing user that is passed within the login_hint structure. If iss_sub format is used, then the user ID is passed within the sub claim. The user ID for a federated connection may have a different format.
request_expiryThe CIBA flow’s requested expiry is between 1 and 300 seconds, and it defaults to 300 seconds. Include the request_expiry parameter to set a custom expiry for the CIBA flow.
binding_messageHuman-readable message used to bind the CIBA flow across the authentication and consumption devices. The binding message is required and up to 64 characters. Use only alphanumeric and +-_.,:# characters
audienceUnique identifier of the audience for the issued token.
authorization_detailsAn optional JSON array of objects that describes the permissions to be authorized. You should register each object’s type value on the resource server using the resource server’s authorization_details parameter. To learn more, read Configure Rich Authorization Requests.

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Step 2: Auth0 tenant acknowledges the CIBA request

If the Auth0 tenant successfully receives the POST request, you should receive a response containing an auth-req-id that references the request: 
{
    "auth_req_id": "eyJh...",
    "expires_in": 300,
    "interval": 5
}
The auth_req_id value is passed to the /token endpoint to poll for the completion of the CIBA flow.

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Step 3: Client application polls for a response

Use the Authentication API to call the /token endpoint using the urn:openid:params:grant-type:ciba grant type and the auth_req_id you received from the /bc-authorize endpoint: 
curl --location 'https://$tenant.auth0.com/oauth/token' \
  --header 'Content-Type: application/x-www-form-urlencoded' \
  --data-urlencode 'client_id=$client_id' \
  --data-urlencode 'client_secret=$client_secret' \
  --data-urlencode 'auth_req_id=$auth_req_id' \
  --data-urlencode 'grant_type=urn:openid:params:grant-type:ciba'
Until the authorizing user approves the transaction, you should receive the following response: 
{
    "error": "authorization_pending",
    "error_description": "The end-user authorization is pending"
}
There is approximately a five-second wait interval for polling. If you poll too frequently, you will receive the following response, where the description varies depending on the backoff interval: 
{
"error": "slow_down",
"error_description": "You are polling faster than allowed. Try again in 10 seconds."
"interval": 10
}
To resolve the error, wait until the next interval (in seconds) to poll the /token endpoint.

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Step 4: Mobile application receives the push notification

Auth0 sends a push notification to the user’s registered mobile app or device. The Guardian SDK provides methods to parse the data received from the push notification and return a ready-to-use Notification instance. The Notification instance includes a transaction linking ID, or txlinkid, that the mobile application uses to retrieve the consent details from Auth0. The following code samples are example iOS and Android mobile push notification implementations using the Guardian SDK: 
//implementing UNUserNotificationCenterDelegate
func userNotificationCenter(_ center: UNUserNotificationCenter, willPresent notification: UNNotification, withCompletionHandler completionHandler: (UNNotificationPresentationOptions) -> Void) {
    let userInfo = notification.request.content.userInfo
    if let notification = Guardian.notification(from: userInfo) {
         // Implement this function to display the prompt and handle user's consent/rejection.
         handleGuardianNotification(notification: notification)
    }
}
Call the Guardian SDK from your mobile application to retrieve the consent details i.e. the contents of the binding_message from the Auth0 Consent API. The following code samples are example iOS and Android implementations that retrieve data from the Auth0 Consent API: 
let device: AuthenticationDevice = // the object you obtained during the initial Guardian SDK enrollment process and stored locally
if let consentId = notification.transactionLinkingId {
    Guardian
        .consent(forDomain: {yourTenantDomain}, device: device)
        .fetch(consentId: consentId, notificationToken: notification.transactionToken)
        .start{result in
            switch result {
            case .success(let payload):
                // present consent details to the user
            case .failure(let cause):
                // something went wrong
        }
    }
}
The Auth0 Consent API responds to the mobile application with the consent details, including the binding_message, scope, audience, and authorization_details if configured. The scopes returned to the mobile application are filtered according to your RBAC policy. To learn more, read Role-Based Access Control. The following code sample is an example response from the Auth0 Consent API: 
{
  "id": "cns_2309dsfsd098",
  "requested_details": {
    "audience": "https://api.example.com",
    "scope": ["read:profile", "write:profile"],
    "binding_message": "abc123",
    "authorization_details": [
      {
        "type": "money_transfer",
        "instructedAmount": {
          "amount": 2500,
          "currency": "USD"
        },
        "sourceAccount": "xxxxxxxxxxx1234",
        "destinationAccount": "xxxxxxxxxxx9876",
        "beneficiary": "Hanna Herwitz",
        "subject": "A Lannister Always Pays His Debts"
      }
    ]
  },
  "created_at": 1632739200,
  "expires_at": 1632739200
}
The mobile application presents the authorization request and/or the consent details with the authorization_details to the user in a push notification via the Guardian SDK. The user can accept or decline the authorization request at this point.

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Step 7: Mobile application sends the user response back to Auth0

Depending on whether the user accepts or rejects the authorization request, the mobile application sends the user response back to Auth0. The following code samples are example iOS and Android implementations that handle the user response:

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User accepts the authorization request

Guardian
    .authentication(forDomain: "{yourTenantDomain}", device: device)
    .allow(notification: notification)
    // or reject(notification: notification, withReason: "hacked")
    .start { result in
        switch result {
        case .success:
            // the auth request was successfully rejected
        case .failure(let cause):
            // something failed, check cause to see what went wrong
        }
    }

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User rejects the authorization request

Guardian
        .authentication(forDomain: "{yourTenantDomain}", device: device)
        .reject(notification: notification)
        // or reject(notification: notification, withReason: "hacked")
        .start { result in
            switch result {
            case .success:
                // the auth request was successfully rejected
            case .failure(let cause):
                // something failed, check cause to see what went wrong
            }
        }

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Step 8: Auth0 receives user response after the flow completes

The client application completes the polling upon receiving a response from the /token endpoint. A CIBA flow always requires a response, either an approval or decline, from the authorizing user, and existing grants are not checked. This means Auth0 treats every CIBA request as a fresh authorization for the authorizing user.

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Step 9: Auth0 returns access token to client application

If the user rejects the push request, Auth0 returns an error response like the following to the client application: 
{
    "error": "access_denied",
    "error_description": "The end-user denied the authorization request or it has been expired"
}
If the user approves the push request, Auth0 returns an with the authorization_details like the following to the client application: 
{
  "id_token": "...",
  "access_token": "...",
  "expires_in": "...",
  "scope": "$granted_scopes",
  "authorization_details": [{
      "type": "money_transfer", 
      "instructedAmount": {
        "amount": 2500, 
        "currency": "USD"
      }, 
      "sourceAccount": "xxxxxxxxxxx1234", 
      "destinationAccount": "xxxxxxxxxxx9876", 
      "beneficiary": "Hanna Herwitz", 
      "subject": "A Lannister Always Pays His Debts"
    }]
}
Note: The id_token will only be present if the openid scope was included in the initial /bc-authorize request.

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Query authorization_details

At compile time, you can query the type and objects of authorization_details from the consent details in a strongly typed manner as you would dynamically query JSON: 
let requestedDetails: ConsentRequestedDetails = payload.requestedDetails
let myAuthorizationDetailsTypes = requestedDetails.authorizationDetails[0].objectValue!;
let type = myAuthorizationDetailsTypes["type"]?.stringValue // Your pre-registered type value
let stringProperty = myAuthorizationDetailsTypes["string_property"]?.stringValue
let boolProperty = myAuthorizationDetailsTypes["bool_property"]?.boolValue
let numericProperty = myAuthorizationDetailsTypes["numeric_property"]?.doubleValue
let nestedObjectProperty = myAuthorizationDetailsTypes["nested_property"]?.objectValue
let nestedArrayProperty = myAuthorizationDetailsTypes["nested_array_property"]?.arrayValue
If you define a custom type to represent your object, you can use the filterAuthorizationDetailsByType() function to return all authorization_details objects that match the desired type. The following code sample queries authorization_details with the payment type: 
// Must implement AuthorizationDetailsType 
struct Payment : AuthorizationDetailsType { 
static let type = "payment"; 
let amount: Double; 
let currency: String; 
} 

... 

let requestedDetails: ConsentRequestedDetails = payload.requestedDetails 
let payments = requestedDetails.filterAuthorizationDetailsByType(Payment.self) 
let firstPayment = payments.first!
let type: String = firstPayment.type // "payment" 
let amount: Double = firstPayment.amount 
let currency: String = firstPayment.currency
filterAuthorizationDetailsByType() only returns objects matching the specified authorization_details type. As a result, your mobile application should present all relevant authorization_details to the user for consent, regardless of their type, to ensure a complete understanding of the request You can also query the authorization_details when the AI agent or application polls the /oauth/tokenendpoint for a response: 
POST https://$tenant/oauth/token
Content-Type: application/x-www-form-urlencoded

grant_type=urn:openid:params:grant-type:ciba&
client_id=$client_id&
client_secret=$client_secret&
auth_req_id=$auth_req_id
ParametersDescription
grant_typeSet to the CIBA grant type: urn:openid:params:grant-type:ciba
client_idSet to the application’s client ID.
client_secretSet to the application’s client secret.
auth_req_idReturned from the Auth0 tenant when it acknowledges the CIBA request. References the CIBA request.
When the authorizing user approves the request, Auth0 receives the user response, and the CIBA flow completes, returning an access token and authorization_details array: 
{ 
  "access_token": "ey...ZQ", 
  "expires_in": 86400, 
  "authorization_details": [{ 
    "type": "money_transfer", 
    "instructedAmount": {
      "amount": 2500, 
      "currency": "USD"
    }, 
    "sourceAccount": "xxxxxxxxxxx1234", 
    "destinationAccount": "xxxxxxxxxxx9876", 
    "beneficiary": "Hanna Herwitz", 
    "subject": "A Lannister Always Pays His Debts" 
  }], 
  "token_type": "Bearer" 
}

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Limitations

Auth0 doesn’t support:
  • Accessing or modifying RAR in Actions for CIBA flows.
  • Advertising RAR types for clients to discover, which means you need to pre-register clients with the authorization_details types they can send.
  • Validating RAR objects beyond checking that they have a type property that matches allowed types for the API. Your resource server is responsible for the granular validation of the content within authorization_details. For more information, see Configure RAR.

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Learn more