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UK Open Banking OIDC Security Profile

Introduction

In many cases, Fintech services such as aggregation services use screen scraping and store user passwords. This model is both brittle and insecure. To cope with the brittleness, it should utilize an API model with structured data and to cope with insecurity, it should utilize a token model such as OAuth [RFC6749, RFC6750].

Financial API aims to rectify the situation by developing a REST/JSON model protected by OAuth. However, just asking to use OAuth is too vague as there are many implementation choices. OAuth is a framework which can cover wide range of use-cases thus some implementation choices are easy to implement but less secure and some implementation choices are harder to implement but more secure. Financial services on the internet is a use-case that requires more secure implementation choices. That is, OAuth needs to be profiled to be used in the financial use-cases.

The Open Banking Profile detailed below outlines the differences between the FAPI R+W profile with clauses and provisions necessary to reduce delivery risk for ASPSPs OP

Notational Conventions

The key words "shall", "shall not", "should", "should not", "may", and "can" in this document are to be interpreted as described in ISO Directive Part 2. These key words are not used as dictionary terms such that any occurence of them shall be interpreted as key words and are not to be interpreted with their natural language meanings.

Financial Services – Open Banking API Security Profile

This document is based on the OpenID Foundations Financial API Read+Write specification document which in turn is based on the Read only specification document. The Open Banking profile will further shape these two base profiles in some cases tightening restrictions and in others loosening requirements using key words 

5. Read and Write API Security Profile

5.2  OB API Security Provisions

5.2.1 Introduction

Open Banking's API Profile does not distinguish between the security requirements from a technical level between "read" and "write" resources. The security requirements for accessing PSU resources held at ASPSPs requires more protection level than a basic RFC6749 supports. 

As a profile of The OAuth 2.0 Authorization Framework, this document mandates the following to the OpenBanking Financial APIs.

5.2.2 Authorization Server

The Authorization Server

• shall support confidential clients;
• shall not support public clients;
• shall support user authentication at appropriate level as defined in PSD2 be that LoA 3 or 2 or other.
• shall require the response_type values code or code id_token or code id_token token;
• shall authenticate the confidential client at the Token Endpoint using one of the following methods:
  1. TLS mutual authentication [MTLS] https://tools.ietf.org/html/draft-ietf-oauth-mtls-05; or (Recommended)
  2. client_secret_basic or client_secret_post provided the client identifier matches the client identifier bound to the underlying mutually authenticated TLS transport session; or (Allowed)
  3. JWS Client Assertion using the client_secret or a private key as specified in section 9 of [OIDC]; (Recommended)
• shall issue an ID Token in the token response when openid was included in the requested scope as in Section 3.1.3.3 of OIDC with its sub value corresponding to the "Intent Ticket ID"  and optional acr value in ID Token.
• may support refresh tokens.

Further, if it wishes to provide the authenticated user's identifier to the client in the token response, the authorization server

• shall issue an ID Token in the token response when openid was included in the requested scope as in Section 3.1.3.3 of [OIDC] with its sub value corresponding to the authenticated user and mandatory acr value in ID Token.
• must support Request Objects passed by value as in clause 6.3 of OIDC.
  
  

5.2.3 Public Client

Open Banking OPs can support Public Clients at their discretion.

Should an OP wish to support public clients all provisions of the FAPI Read Write API security profile will be adhered too with exceptions below;

• shall request user authentication at appropriate level as defined in PSD2 be that LoA 3 or 2 or other.

5.2.4 Confidential Client

 A Confidential Client

• may use separate and distinct Redirect URI for each Authorization Server that it talks to;
• shall support the following methods to authenticate against the Token Endpoint:
  • TLS mutual authentication [MTLS]; or
  • JWS Client Assertion using the client_secret or a private key as specified in section 9 of [OIDC]; or
  • client_secret_basic or client_secret_post provided the client identifier matches the client identifier bound to the underlying mutually authenticated TLS transport session
• shall accept signed ID Tokens; 

6. Accessing Protected Resources

6.2 Access provisions

6.2.1 Protected resources provisions

The resource server with the FAPI endpoints

• shall mandate mutually authenticated TLS 1.2 or later as defined in RFC5246 with the usage following the best practice in RFC7525;
• shall verify that the client identifier bound to the underlying mutually authenticated TLS transport session matches the client that the access token was issued to;

6.3 Client provisions

The confidential client supporting this document

• shall use mutually authenticated TLS 1.2 or later as defined in RFC5246 with the usage following the best practice in RFC7525;

• shall supply the last time the customer logged into the client in the x-fapi-customer-last-logged-time header where the value is supplied as ** w3c date **, e.g., x-fapi-customer-last-logged-time: Tue, 11 Sep 2012 19:43:31 UTC; and
• shall supply the customer’s IP address if this data is available or applicable in the x-fapi-customer-ip-address header, e.g., x-fapi-customer-ip-address: 198.51.100.119; and
• shall send x-fapi-financial-id whose value is the unique identifier of the financial institution assigned by OpenBanking.

Further, the client

• may supply the customers authentication context reference (ACR) or applicable in the x-fapi-customer-acr header, e.g., x-fapi-customer-acr; 

7. Request object endpoint

7.1 Introduction

• OPs may not support request_uri, OIDC Request Object by Reference.
• OPs must support Request Objects passed by value as in clause 6.3 of OIDC.

8. Security Considerations

8.1 TLS Considerations

Since confidential information is being exchanged, all interactions shall be encrypted with TLS/SSL (HTTPS) in accordance with the recommendations in RFC7525. TLS version 1.2 or later shall be used for all communications.

8.2 Message source authentication failure and message integrity protection failure

It is not mandated that the Authorization request and response are authenticated. Use of request object for the Authorization request and returning an ID token in the Authorization response should be considered to provide message source authentication and integrity protection.

8.3 Message containment failure

8.3.1 Authorization request and response

In this document, the authorization request is not encrypted. Thus, it is possible to leak the information contained if the browser was infected with virus, etc.

Authorization response can be encrypted if an ID token is returned as ID tokens can be encrypted.

It is possible to leak the information through the logs if the parameters were recorded in the logs and the access to the logs are compromised. Strict access control to the logs in such cases should be enforced.

8.3.2 Token request and response

It is possible to leak the information through the logs if the parameters were recorded in the logs and the access to the logs are compromised. Strict access control to the logs in such cases should be enforced.

8.3.3 Resource request and response

Care should be taken so that the sensitive data will not be leaked through the referrer.

If the access token is a bearer token, it is possible to exercise the stolen token. Since the access token can be used against multiple URIs, the risk of its leaking is much larger than the refresh token, which is used only against the token endpoint. Thus, the lifetime of the access token should be much shorter than that of the refresh token. Refer to section 16.18 of OIDC for more discussion on the lifetimes of access tokens and refresh tokens.

Security Architecture

OAuth 2.0, OIDC and FAPI

OAuth 2.0 will be the foundational framework for API Security in OpenBanking.  The process of requesting a token is standards based - the question is, which standards.  OAuth 2.0 itself is a framework which can be deployed in many ways, some of them completely incompatible with financial models. In order to securely use the OAuth 2.0 framework, a profile must exist by which both TPP and ASPSP participants are certified to have correctly configured their clients and servers.  The Financial API working group in the OpenID Foundation has created a draft standard for configuration of financial grade API security regimes, and it is strongly recommended that OpenBanking follow that standard.  If any FAPI-compliant vendor can participate in the OpenBanking ecosystem, it means that vendors can work to the standard and reach many customers, rather than having to create different solutions for different banking platforms. 

Consuming PSU owned Resources from an ASPSP

Overview

See:  http://openid.net/specs/openid-connect-core-1_0.html#JWTRequests (OpenID Connect Core Section 6)

The OpenID Connect Request object uses exactly the same claims object for specifying claim names, priorities, and values, however if the request object is used, the claims object becomes a member in an assertion that can be signed and encrypted, allowing the ASPSP to authenticate the request from the TPP and ensure it hasn't been tampered with.  The OpenID Connect request object can either be passed as a query string parameter, or can be referenced at an endpoint that could theoretically be protected by MATLS. OpenBanking, in conjuction with major IAM vendors, is ruling out the use of JWT Request objects by reference due a number of delivery risks and remaining security concerns.

In addition to specifying a ticket, the TPP can optionally require a minimum strength of authentication context or request to know how long ago the user was actually authenticated.  Multiple tickets could be passed if necessary.  Everything is fully specified. Vendors who implement this feature are not creating a one-off proprietary feature, they are simply supporting the OpenID Connect standard.

Full accountability is available as required by all participants. Not only can the ASPSP prove that they received the original request from the TPP, but the TPP can prove that the access token that comes back was the token that was intended to be affiliated to this specific payment.

Hybrid Flow Request with Intent Id

This section describes parameters that should be used with an hybrid grant flow request so that an intent id can be passed from the TPP to an ASPSP.

Prior to this step, 

1. The TPP would have already registered an intent with an ASPSP. This is achieved by using one of the account information or payment initiation APIs.
2. The ASPSP would have responsded with an intent id.

Hybrid Grant Parameters

Minimum Conformance

Overview

This section describes the bare minimum set of Authorization Request parameters that an ASPSP must support for the Jan, 2018 release. The technical definitive reference is specified in OpenID Connect Core Errata 1 Section 6.1 (Request Object). All standards and guidance MUST be followed as per the specification.

All ASPSPs MUST support the issuance of OIDC ID Tokens, a TPP MAY request that an ID token is issued. 

Example for minimum conformance

Examples are non-normative

HTTP Request

Request JWS (Without Base64 encoding)

Note that "essential" is an optional required OPTIONAL. Indicates whether the Claim being requested is an Essential Claim. If the value is true, this indicates that the Claim is an Essential Claim. For instance, the Claim request:

  "auth_time": {"essential": true}

can be used to specify that it is Essential to return an auth_time Claim Value.If the value is false, it indicates that it is a Voluntary Claim. The default is false.By requesting Claims as Essential Claims, the RP indicates to the End-User that releasing these Claims will ensure a smooth authorization for the specific task requested by the End-User. Note that even if the Claims are not available because the End-User did not authorize their release or they are not present, the Authorization Server MUST NOT generate an error when Claims are not returned, whether they are Essential or Voluntary, unless otherwise specified in the description of the specific claim. OIDC Core

id_token returned - Sub being populated with an EphemeralId of the IntentId - Non Normative

id_token returned - Identity Claims and IntentId With sub being populated with an UserIdentifier - Non Normative

 ID Token Claims Details: Where appropriate please follow the JWT Good Practice Guides http://self-issued.info/docs/draft-sheffer-oauth-jwt-bcp-00.html#rfc.section.3.1 

JSON Security Suite Information v1.0

General Guidance for JWT Best Practice: To Be Followed Where Appropriate

http://self-issued.info/docs/draft-sheffer-oauth-jwt-bcp-00.html#rfc.section.3.1

Algorithms to be supported: All Asymmetric Algorithms listed below

• TLS_DHE_RSA_WITH_AES_128_GCM_SHA256
• TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256
• TLS_DHE_RSA_WITH_AES_256_GCM_SHA384
• TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384

JWKS Endpoints

All JWKS endpoints will be hosted by OpenBanking Ltd. Upon issuance of a certificate a JWK Set will be created or updated for a given TPP.

All participants should include "kid" and "jku" of the key that was used to sign the payloads. The JKU should be considered a hint only and relying parties should derive and then validate wherever possible the appropriate JWKS endpoint for the message signer.

https://tools.ietf.org/html/draft-ietf-jose-json-web-signature-41#section-4.1

example:

https://keystore.openbanking.org.uk/tpp/12345678.jwks

As certificates are added and removed by Participant Technical Contacts the jwks endpoint will be updated automatically.

General outline for creating a JWS

Step 1: Select the certificate and private key that will be used for signing the JWS

As the JWS is used for non-repudiation, it MUST be signed using one of JWS issuer's private keys.

The private key MUST have been used by the issuer to get a signing certificate issued from OB. 

The signing certificate MUST be valid at the time of creating the JWS.

Step 2: Form the JOSE Header

The JOSE header is a JSON object consisting of three fields (claims):

   The "kid" (key ID) Header Parameter is a hint indicating which key
   was used to secure the JWS. 

Step 3: Form the payload to be signed

The JSON payload to be signed must have the following claims:

The payload to be signed is computed as:

Where:

JOSEHeader: is the header created in Step 2 and

json: is the message the original data to be sent

Step 4: Sign and encode the payload

The signed payload is computed as:

Where:

privateKey: is the private key selected in step 1

payload: is the payload computed in Step 3

encrypt: Is an encryption function that implements the `alg` identified in Step 2.

Step 5: Assemble the JWS

The JWS is computed as

Where:

payload: is the payload computed in Step 3

signedAndEncodedPayload: is the signed element computed in Step 5.

Implementation Guide

Overview

This page provides an implementation perspective of the OB Security Profile aligned to the accepted OB Read/Write APIs for Payments and Accounts Specifications.

Specified Behaviour

The implementation of both the Payments and Accounts API are based on the following known configurations:

Client Types

• As per the OAuth 2.0 specification, the Confidential Client Type is illustrated for both Accounts and Payments API as it has the ability to maintain its own credentials.

Grant Types

OIDC Hybrid Flow (response_type=code id_token)

• Both the Payments and Accounts APIs illustrate the use of request_type=code id_token for the OIDC Hybrid Flow implementation.    
• The ASPSP may optionally choose to return Refresh Tokens for the Hybrid Flow when issuing an Access Token

Client Credentials Grant Type using multiple scopes (scope=accounts payments)

• The Client Credentials Grant Type is used across both Payments and Account APIs only when the TPP (AISP/PISP) requires an Access Token (on behalf of itself) in order to access a Payment or Accounts API resource e.g.
  

  • Payments:

    POST /payments
    GET /payment-submissions/{PaymentSubmissionId}

  • Accounts: 

    POST /account-requests

• Where an ASPSP enables the same Confidential Client  (ClientId) access to both Payments and Accounts APIs, a TPP may therefore choose to request for either a single scope e.g. accounts or for multiple scope(s) e.g. accounts payments as the TPP may want to use the same Access Token across both APIs. 
• Only valid API scopes will be accepted when generating an Access Token (accounts payments). 
• Access tokens generated by a Client Credentials grant may not return any refresh tokens (as per the OAuth 2.0 specification)

Access Tokens

• For the Payments and Accounts APIs, the Access Token must be obtained within a Secure, Server Side Context between the TPP (AISP / PISP) and the ASPSP. 
• Access Tokens must be validated by the TPP (AISP/PISP) as outlined within the OIDC Errata 1 Specification

Refresh Tokens

• ASPSPs may optionally return a Refresh Token when an Authorization Request is successfully processed at the Token endpoint. The Hybrid flow supports the provisioning of Refresh Tokens.
• The Accounts API implementation below cites an example for AISPs requesting a Refresh Token to refresh an expired Access Token prior to invoking the /accounts resource.
• Refresh Tokens must be validated as outlined in the OIDC Errata 1 Specification

ID Tokens 

• ID Tokens must be validated by the TPP (AISP/PISP) as outlined within the OIDC Errata 1 Specification
• TPPs must use the openbanking_intent_id claim to populate and retrieve the IntentID (PaymentID for Payments API and AccountRequestId for the Accounts API) for any required validation.
• The full set of claims that can be represented within an ID Token are documented in the Request Object and ID Token Section of the Security Profile.

Authorization Codes

• Authorization Codes must be validated by the TPP (AISP/PISP) as outlined within the OIDC Errata 1 Specification

Un-Specified Behaviour

The implementation of both the Payments and Accounts API are un-specified for the following configurations: 

Client Types

• As per the OAuth 2.0 specification, the Public Client Type has not been illustrated for both Payments and Accounts APIs.
  
  

Grant Types

OIDC Hybrid Flow (response_type=code id_token token or response_type=code token)

• Forces an Access Token to be returned from the ASPSP Authorization endpoint (instead of a token endpoint). This is not illustrated in the Payments and Accounts API Specifications.

OIDC Implicit Flow (response_type=id_token token or response_type=id_token)

• The Implicit Flow does not authenticate the Client that is invoking the request. This is not illustrated in the Payments and Accounts API Specifications.

Client Credentials Grant Type(scope=openid email profile address phone)

• Requesting OIDC specific scopes or any un-specified scopes when using the Client Credentials grant. 

Validity Lengths (Authorization Code, Access Token, ID Token, Refresh Token)

These are to be managed in the competitive space; Each ASPSP's Authorization / Resource Server will be configured independently to comply with internal ASPSP Security Policies and Guidelines. The Accounts and Payments API Specifications do not mandate validity lengths. 

Authorization Code

•  OAuth 2.0 Specification suggests an Authorization Code should be short lived to a maximum of 10 minutes. Any codes exceeding this limit to be rejected.

ID Token

• ID Token claims (exp and iat) determine its validity.

• Returned with the Authorization Code when the Hybrid flow (code id_token) is initiated.

Access Token

• The expires_in attribute returned by the Authorization Server when an Access Token is generated determines its validity.
• Access Tokens are generally short lived, and where they expire, are then exchanged for another using a longer lived Refresh Token.
• Refer to Section 16.18 of the OIDC Specification  - Lifetimes of Access Tokens and Refresh Tokens.

Refresh Token

• The expires_in attribute returned by the Authorization Server when a Refresh Token is generated determines its validity.
• Refresh Tokens are generally longer lived in comparison to Access Tokens.
• Refer to Section 16.18 of the OIDC Specification  - Lifetimes of Access Tokens and Refresh Tokens.

Success Flows

Payment API Specification

The sequence diagram below highlights the OAuth 2.0 Client Credentials Grant and OIDC Hybrid flow that are used by the Payments API. 

participant PSU
participant PISP
participant ASPSP Authorisation Server
participant ASPSP Resource Server
   
autonumber 1
    
PSU -> PISP: Establish TLS 1.2
    
note over PSU, ASPSP Resource Server
Step 1: Request payment initiation
end note
PSU -> PISP: Send payment initiation request
     
note over PSU, ASPSP Resource Server
 Step 2: Setup single payment initiation
end note
    
    PISP <-> ASPSP Authorisation Server: Establish TLS 1.2 MA
    note left of PISP
        Client Credentials Grant
    end note
    PISP->ASPSP Authorisation Server: POST /token (client authentication credentials, scope:payments)
    ASPSP Authorisation Server->ASPSP Authorisation Server: Validate client authentication credentials, scope
    ASPSP Authorisation Server->ASPSP Authorisation Server: Validate clientId matches client SSL cert
    ASPSP Authorisation Server -> PISP: HTTP 200 (OK) access-token (scope:payments)
        
    
    PISP <-> ASPSP Resource Server: Establish TLS 1.2 MA
    PISP -> ASPSP Resource Server: POST /payments (access-token - scope:payments)
    ASPSP Resource Server->ASPSP Resource Server: Validate access token
    ASPSP Resource Server->ASPSP Resource Server: Validate scope:payments
    ASPSP Resource Server->ASPSP Resource Server: Validate clientId matches client SSL cert
       
    ASPSP Resource Server->ASPSP Resource Server: Create new payment resource
    ASPSP Resource Server->ASPSP Resource Server: Bind PaymentId with ClientId
    ASPSP Resource Server -> PISP: HTTP 201 (Created),  PaymentId
    
    note right of PISP
        Begin OIDC Hybrid Flow.
        See 6.1.  Passing a Request Object by Value
        See 5.5.  Requesting Claims using the "claims" Request Parameter
        The claims parameter must at least request:
             "id_token": {
       "openbanking_intent_id": {"value": PaymentId, "essential": true},
       "acr": {"essential": true}
      }
      The response object must be signed using the PISP's private key.
    end note
    PISP->PISP: Persist PaymentId
    note right of PISP
        The PISP should store the PaymentId in a manner
        that it can be retrieved again later in the flow in Step 4.
           
        This could be stored in the user session (and retrieved using 'state'
        as a key) or the PSU could use some other unique identifier.
           
        This will be re-retrieved in [43].
           
    end note
    PISP->PISP: Create signed request object with requested Claims (PaymentId)
    PISP -> PSU: HTTP 302 (Found); Location: /authorize,\nredirect-uri, clientId, state, nonce, scope=openid payments,\nresponse-type=code id_token,\nrequest=signed JWT request object - PaymentId)
    
note over PSU, ASPSP Resource Server
 Step 3: Authorize consent
end note
    
PSU -> ASPSP Authorisation Server: HTTP GET /authorize redirect-uri, clientId, state, nonce, scope=openid payments, response-type=code id_token,\nrequest=signed JWT request object - PaymentId
ASPSP Authorisation Server->ASPSP Authorisation Server: Validate clientid, scope
ASPSP Authorisation Server->ASPSP Authorisation Server: Validate redirect-uri for clientId
ASPSP Authorisation Server->ASPSP Authorisation Server: Validate JWT request claim -PaymentId
    note right of ASPSP Authorisation Server
        Validate the request object by using the PISP's public key.
        PISP certificate will be identified using the kid claim
        in the JOSE header of the request object.
           
        Check that the PaymentId belongs to the ClientId that initiated the request.
    end note
ASPSP Authorisation Server<->PSU: Authenticate (Login and consent page)
PSU <-> ASPSP Authorisation Server: SCA if required
PSU <-> ASPSP Authorisation Server: Select debtor account
ASPSP Authorisation Server->ASPSP Authorisation Server: Generate authorization-code, id_token
note right of ASPSP Authorisation Server
    id_token claims:{
    c_hash: 123,
    s_hash: 456
    }
    id_token must be signed using the ASPSP's private key.
    The generation of c_hash is documented in OIDC: 3.3.2.11.  ID Token
    The generation of s_hash is in FAPI R/W spec: Section 5.1
    http://openid.net/specs/openid-financial-api-part-2-wd-02.html#introduction
end note
   
ASPSP Authorisation Server -> PSU: HTTP 302 (Found); Location: redirect-uri (authorization-code, id_token, state)
PSU -> PISP: HTTP GET redirect-uri (authorization-code, id_token, state)
PISP->PISP: Validate signature on id_token
note right of PISP
    Validate the id_token by using the ASPSP's public key.
    ASPSP certificate will be identified using the kid claim
    in the JOSE header of the id_token
end note
PISP->PISP: Validate authorization-code using id_token (c_hash)
PISP->PISP: Validate state using id_token (s_hash)
PISP->PISP: Validate nonce using id_token
    
    
note right of PISP:
    Exchange authorization-code for access token.
end note
PISP <-> ASPSP Authorisation Server: Establish TLS 1.2 MA
PISP -> ASPSP Authorisation Server: HTTP POST /token (client authentication credentials,\nauthorization-code, grant_type, redirect_uri)
    ASPSP Authorisation Server->ASPSP Authorisation Server: Validate clientId matches client SSL cert
    ASPSP Authorisation Server->ASPSP Authorisation Server: Validate client authentication credentials,\nauthorization-code
    ASPSP Authorisation Server->ASPSP Authorisation Server: Generate access-token
    ASPSP Authorisation Server->ASPSP Authorisation Server: Bind access-token to PaymentId
       
ASPSP Authorisation Server -> ASPSP Resource Server: Update Payment Status to AcceptedCustomerProfile
ASPSP Resource Server -> ASPSP Authorisation Server: OK
note right of ASPSP Authorisation Server
    Implementation of how the resource is updated is ASPSP specific. (There is
    no standardised API for this)
end note
   
   
ASPSP Authorisation Server -> PISP: HTTP 200 (OK) access-token (scope:payments)
     
       
note over PSU, ASPSP Resource Server
Step 4: Create payment submission
end note
PISP <-> ASPSP Resource Server: Establish TLS 1.2 MA
PISP->PISP: Retrieve PaymentId
note left of PISP
    Retrieve the PaymentId that was issued in Step 2.
    The method for doing this will depend on how the PISP persisted
    the payment id in [16]
       
end note
   
alt Validate PaymentId in  ID Token
    PISP->PISP: Decode / verify ID Token
    PISP->PISP: Read PaymentId from id_token claim
    PISP->PISP: Compare with PaymentId retrieved in [43]
else Validate PaymentId from UserInfo endpoint
    PISP->ASPSP Resource Server: GET /userInfo (access-token)
    ASPSP Resource Server->ASPSP Resource Server: Validate access-token matches client SSL cert
    ASPSP Resource Server->ASPSP Resource Server: Validate access-token
    ASPSP Resource Server->PISP: HTTP 200 (OK) - UserInfo claim - PaymentId
end
PISP -> ASPSP Resource Server: POST /payment-submissions (access-token - scope:payments) using PaymentId
    ASPSP Resource Server->ASPSP Resource Server: Validate access-token
    ASPSP Resource Server->ASPSP Resource Server: Validate access-token matches client SSL cert
    ASPSP Resource Server->ASPSP Resource Server: Validate scope:payments
    note right of ASPSP Resource Server
        Check binding created in [38]
    end note
    ASPSP Resource Server->ASPSP Resource Server: Ensure access-token is bound to PaymentId
    ASPSP Resource Server->ASPSP Resource Server: Update payment status to AcceptedSettlementInProcess
ASPSP Resource Server -> PISP: HTTP 201 (Created), PaymentSubmissionId
     
note over PSU, ASPSP Resource Server
Step 5: Get payment submission status
end note
     
opt
    PISP <-> ASPSP Resource Server: Establish TLS 1.2 MA
    alt Use active access token to retrieve payment status
        PISP -> ASPSP Resource Server: GET /payment-submissions/{PaymentSubmissionId} (access-token - scope:payments)
        ASPSP Resource Server->ASPSP Resource Server: Validate access-token
        ASPSP Resource Server->ASPSP Resource Server: Validate access-token matches client SSL cert
        ASPSP Resource Server->ASPSP Resource Server: Validate scope:payments
        ASPSP Resource Server->PISP: HTTP 200 (OK), payment-submissions resource
    else Initiate fresh access token via client credentials grant
        note left of PISP
            Client Credentials Grant
        end note
        PISP->ASPSP Authorisation Server: POST /token (client authentication credentials, scope:payments)
        ASPSP Authorisation Server->ASPSP Authorisation Server: Validate client authentication credentials, scope
        ASPSP Authorisation Server->ASPSP Authorisation Server: Validate clientId matches client SSL cert
        ASPSP Authorisation Server -> PISP: HTTP 200 (OK) access-token (scope:payments)
        PISP -> ASPSP Resource Server: GET /payment-submissions/{PaymentSubmissionId} (access-token - scope:payments)
        ASPSP Resource Server->ASPSP Resource Server: Validate access-token
        ASPSP Resource Server->ASPSP Resource Server: Validate access-token matches client SSL cert
        ASPSP Resource Server->ASPSP Resource Server: Validate scope:payments
        ASPSP Resource Server->PISP: HTTP 200 (OK), payment-submissions resource
    end alt
end opt

Client Credentials Grant Type (OAuth 2.0)

Summary

This grant type is used by the PISP in Step 2 to setup a single payment with the ASPSP.

1. The PISP initiates an Authorization request using valid Client Credentials Grant type and scope(s)
2. The ASPSP Authorization Server validates the Client Authentication request from the PISP and generates an Access Token response where the request is valid
3. The PISP uses the Access Token to create a new Payment resource against the ASPSP Resource Server
4. The ASPSP Resource server responds with the PaymentId for the resource it has created. 
5. The Client Credentials Grant may optionally be used by the PISP in Step 5 to retrieve the status of a Payment or Payment-Submission where no active Access Token is available.
   
   
   

OIDC Hybrid Flow

Summary

• The Hybrid flow is the recommendation from the OB Security Profile and the FAPI Specification for R/W. The Hybrid flow prevents IdP mixup attacks as documented by Nat Sakimura - Cut and Paste OAuth 2.0 Attack
• This is initiated at the end of Step 2 by the PISP after the PaymentId is generated by the ASPSP and returned to the PISP.
• This is used in a redirect across the PSU and ASPSP in Step 3 in order for the PSU to authorize consent with the ASPSP - for the PISP to proceed with the Payment.
• This is used across the PISP and ASPSP in Step 4 by exchanging the Authorization Code for an Access Token in order to create the Payment-Submission resource.
  
  

Non-Normative HTTP Request and Response Examples

Step 1 - Request Payment Initiation

There are no Requests and Responses against the Payments API in this Step for the PSU, PISP and ASPSP.

Step 2 - Setup Single Payment Initiation

1. PISP obtains an Access Token using a Client Credentials Grant Type. The scope payments must be used. When an Access Token expires, the PISP will need to re-request for another Access Token using the same request below. 

POST  /as/token.oauth2 HTTP/1.1
Host: https://authn.alphabank.com
Content-Type: application/x-www-form-urlencoded
Accept: application/json
grant_type=client_credentials
&scope=payments
&client_assertion_type=
    urn%3Aietf%3Aparams%3Aoauth%3Aclient-assertion-type%3Ajwt-bearer
&client_assertion=eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9.eyJpc3MiOiJodHRw
czovL2p3dC1pZHAuZXhhbXBsZS5jb20iLCJzdWIiOiJtYWlsdG86bWlrZUBleGFtcGxlLmN
vbSIsIm5iZiI6MTQ5OTE4MzYwMSwiZXhwIjoxNDk5MTg3MjAxLCJpYXQiOjE0OTkxODM2MD
EsImp0aSI6ImlkMTIzNDU2IiwidHlwIjoiaHR0cHM6Ly9leGFtcGxlLmNvbS9yZWdpc3Rlc
iJ9.SAxPMaJK_wYl_W2idTQASjiEZ4UoI7-P2SbmnHKr6LvP8ZJZX6JlnpK_xClJswAni1T
p1UnHJslc08JrexctaeEIBrqwHG18iBcWKjhHK2Tv5m4nbTsSi1MFQOlMUTRFq3_LQiHqV2
M8Hf1v9q9YaQqxDa4MK0asDUtE_zYMHz8kKDb-jj-Vh4mVDeM4_FPiffd2C5ckjkrZBNOK0
01Xktm7xTqX6fk56KTrejeA4x6D_1ygJcGfjZCv6Knki7Jl-6MfwUKb9ZoZ9LiwHf5lLXPuy
_QrOyM0pONWKj9K4Mj7I4GPGvzyVqpaZUgjcOaZY_rlu_p9tnSlE781dDLuw

{
  "alg": "RS256",
  "kid": "12345",
  "typ": "JWT"
}
.
{
  "iss": "s6BhdRkqt3",
  "sub": "s6BhdRkqt3",
  "exp": 1499187201,
  "iat": 1499183601,
  "jti": "id123456",
  "aud": "https://authn.alphabank.com/as/token.oauth2"
}
.
<<signature>>

Content-Length: 1103
Content-Type: application/json
Date: Mon, 26 Jun 2017 15:18:28 GMT
{
    "access_token": "2YotnFZFEjr1zCsicMWpAA",
    "expires_in": 3600,
    "token_type": "bearer",
	"scope":"payments"
}

2. PISP uses the Access Token (with payments scope) from the ASPSP to invoke the Payments API.  This example is sourced directly from the Payment API Specification

POST /payments HTTP/1.1
Authorization: Bearer 2YotnFZFEjr1zCsicMWpAA
x-idempotency-key: FRESCO.21302.GFX.20
x-fapi-financial-id: OB/2017/001
x-fapi-customer-last-logged-time: 2017-06-13T11:36:09
x-fapi-customer-ip-address: 104.25.212.99
x-fapi-interaction-id: 93bac548-d2de-4546-b106-880a5018460d
Content-Type: application/json
Accept: application/json
 
{
  "Data": {
    "Initiation": {
      "InstructionIdentification": "ACME412",
      "EndToEndIdentification": "FRESCO.21302.GFX.20",
      "InstructedAmount": {
        "Amount": "165.88",
        "Currency": "GBP"
      },
      "CreditorAccount": {
        "SchemeName": "SortCodeAccountNumber",
        "Identification": "08080021325698",
        "Name": "ACME Inc",
        "SecondaryIdentification": "0002"
      },
      "RemittanceInformation": {
        "Reference": "FRESCO-101",
        "Unstructured": "Internal ops code 5120101"
      }
    }
  },
  "Risk": {
    "PaymentContextCode": "EcommerceGoods",
    "MerchantCategoryCode": "5967",
    "MerchantCustomerIdentification": "053598653254",
    "DeliveryAddress": {
      "AddressLine": [
        "Flat 7",
        "Acacia Lodge"
      ],
      "StreetName": "Acacia Avenue",
      "BuildingNumber": "27",
      "PostCode": "GU31 2ZZ",
      "TownName": "Sparsholt",
      "CountySubDivision": [
        "Wessex"
      ],
      "Country": "UK"
    }
  }
}

HTTP/1.1 201 Created
x-fapi-interaction-id: 93bac548-d2de-4546-b106-880a5018460d
Content-Type: application/json
 
{
  "Data": {
    "PaymentId": "58923",
    "Status": "AcceptedTechnicalValidation",
    "CreationDateTime": "2017-06-05T15:15:13+00:00",
    "Initiation": {
      "InstructionIdentification": "ACME412",
      "EndToEndIdentification": "FRESCO.21302.GFX.20",
      "InstructedAmount": {
        "Amount": "165.88",
        "Currency": "GBP"
      },
      "CreditorAccount": {
        "SchemeName": "SortCodeAccountNumber",
        "Identification": "08080021325698",
        "Name": "ACME Inc",
        "SecondaryIdentification": "0002"
      },
      "RemittanceInformation": {
        "Reference": "FRESCO-101",
        "Unstructured": "Internal ops code 5120101"
      }
    }
  },
  "Risk": {
    "PaymentContextCode": "EcommerceGoods",
    "MerchantCategoryCode": "5967",
    "MerchantCustomerIdentification": "053598653254",
    "DeliveryAddress": {
      "AddressLine": [
        "Flat 7",
        "Acacia Lodge"
      ],
      "StreetName": "Acacia Avenue",
      "BuildingNumber": "27",
      "PostCode": "GU31 2ZZ",
      "TownName": "Sparsholt",
      "CountySubDivision": [
        "Wessex"
      ],
      "Country": "UK"
    }
  },
  "Links": {
    "Self": "https://api.alphabank.com/open-banking/v1.0/payments/58923"
  },
  "Meta": {}
}

Step 3 - Authorize Consent

1. PISP receives a PaymentId from the ASPSP. The PISP then creates an Authorization request (using a signed JWT Request containing the PaymentID as a claim) for the PSU to consent to the Payment directly with their ASPSP. The request is an OIDC Hybrid flow (requesting for Code and id_token)

GET /authorize?
response_type=code id_token
&client_id=s6BhdRkqt3
&state=af0ifjsldkj
&scope=openid payments
&nonce=n-0S6_WzA2Mj
&redirect_uri=https://api.mytpp.com/cb
&request=CJleHAiOjE0OTUxOTk1ODd.....JjVqsDuushgpwp0E.5leGFtcGxlI
iwianRpIjoiM....JleHAiOjE0.olnx_YKAm2J1rbpOP8wGhi1BDNHJjVqsDuushgpwp0E

{
    "alg": "",
    "kid": "GxlIiwianVqsDuushgjE0OTUxOTk"
}
.
{
   "iss": "https://api.alphabank.com",
   "aud": "s6BhdRkqt3",
   "response_type": "code id_token",
   "client_id": "s6BhdRkqt3",
   "redirect_uri": "https://api.mytpp.com/cb",
   "scope": "openid payments accounts",
   "state": "af0ifjsldkj",
   "nonce": "n-0S6_WzA2Mj",
   "max_age": 86400,
   "claims":
    {
     "userinfo":
      {
       "openbanking_intent_id": {"value": "urn:alphabank:intent:58923", "essential": true}
      },
     "id_token":
      {
       "openbanking_intent_id": {"value": "urn:alphabank:intent:58923", "essential": true},
       "acr": {"essential": true,
				"values": ["urn:openbanking:psd2:sca",
                     "urn:openbanking:psd2:ca"]}}}
      }
    }
}
.
<<signature>>

HTTP/1.1 302 Found
  Location: https://api.mytpp.com/cb#
    code=SplxlOBeZQQYbYS6WxSbIA
    &id_token=eyJ0 ... NiJ9.eyJ1c ... I6IjIifX0.DeWt4Qu ... ZXso
    &state=af0ifjsldkj

2. The PSU is then redirected to the PISP. The PISP will now possess the Authorization Code and ID Token from the ASPSP. Note at this point, there is no Access Token. The PISP will now introspect the ID Token and use it as a detached signature to check:

• The hash of the Authorization Code to prove it hasn't been tampered with during redirect (comparing the hash value against the c_hash attribute in ID Token)
• The hash of the State to prove it hasn't been tampered with during redirect (comparing the state hash value against the s_hash attribute in the ID Token)

3. Once the state and code validations have been confirmed as successful by use of the ID token, the PISP will proceed to obtain an Access Token from the ASPSP using the Authorization Code they now possess. The PISP will present its Authorization Code together with the private_key_jwt. The Access Token is required by the PISP in order to submit the Payment on behalf of the PSU. The payments scope should already be associated with the Authorization Code generated in the previous step.

POST /as/token.oauth2 HTTP/1.1
Host: https://authn.alphabank.com
Content-Type: application/x-www-form-urlencoded
Accept: application/json
grant_type=authorization_code
&code=SplxlOBeZQQYbYS6WxSbIA
&redirect_uri=https://api.mytpp.com/cb
&client_assertion_type=
    urn%3Aietf%3Aparams%3Aoauth%3Aclient-assertion-type%3Ajwt-bearer
&client_assertion=eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9.eyJpc3MiOiJodHRw
czovL2p3dC1pZHAuZXhhbXBsZS5jb20iLCJzdWIiOiJtYWlsdG86bWlrZUBleGFtcGxlLmN
vbSIsIm5iZiI6MTQ5OTE4MzYwMSwiZXhwIjoxNDk5MTg3MjAxLCJpYXQiOjE0OTkxODM2MD
EsImp0aSI6ImlkMTIzNDU2IiwidHlwIjoiaHR0cHM6Ly9leGFtcGxlLmNvbS9yZWdpc3Rlc
iJ9.SAxPMaJK_wYl_W2idTQASjiEZ4UoI7-P2SbmnHKr6LvP8ZJZX6JlnpK_xClJswAni1T
p1UnHJslc08JrexctaeEIBrqwHG18iBcWKjhHK2Tv5m4nbTsSi1MFQOlMUTRFq3_LQiHqV2
M8Hf1v9q9YaQqxDa4MK0asDUtE_zYMHz8kKDb-jj-Vh4mVDeM4_FPiffd2C5ckjkrZBNOK0
01Xktm7xTqX6fk56KTrejeA4x6D_1ygJcGfjZCv6Knki7Jl-6MfwUKb9ZoZ9LiwHf5lLXPuy
_QrOyM0pONWKj9K4Mj7I4GPGvzyVqpaZUgjcOaZY_rlu_p9tnSlE781dDLuw

{
  "alg": "RS256",
  "kid": "12345",
  "typ": "JWT"
}
.
{
  "iss": "s6BhdRkqt3",
  "sub": "s6BhdRkqt3",
  "exp": 1499187201,
  "iat": 1499183601,
  "jti": "id123456",
  "aud": "https://authn.alphabank.com/as/token.oauth2"
}
.
<<signature>>

  HTTP/1.1 200 OK
  Content-Type: application/json
  Cache-Control: no-store
  Pragma: no-cache

  {
   "access_token": "SlAV32hkKG",
   "token_type": "Bearer",
   "expires_in": 3600
  }

Step 4 - Create Payment-Submission

1. The PISP has an Access Token which can be used to Create a Payment-Submission (Step 4). The PISP must obtain the PaymentId (Intent-ID) so that the Payment request is associated with the correct PaymentId. This can be sourced from either:

1. The PaymentId claim from the signed ID Token (default). The PISP will need to decode the ID Token JWT and locate the claim attribute associated with the PaymentId.
2. The PaymentId claim from the /userInfo resource endpoint of the ASPSP (optional for ASPSPs to implement) .

The example below provides an illustration of the PISP requesting the /userInfo endpoint of the ASPSP in order to get the PaymentID (returned as openbanking_intent_id)

GET /userinfo HTTP/1.1
  Host: api.alphabank.com
  Authorization: Bearer SlAV32hkKG

  HTTP/1.1 200 OK
  Content-Type: application/json

  {
   "sub": "PSU User Id",
   "openbanking_intent_id": [ "IntentId:1", "IntentId:2" ],
   "name": "Open Banking",
   "given_name": "Open Banking",
   "family_name": "Open Banking",
   "preferred_username": "Open Banking",
   "email": "Open Banking@example.com",
   "picture": "http://example.com/janedoe/me.jpg"
  }

2. The PISP can now invoke the /payment-submissions endpoint to commit the Payment using the Access Token and PaymentId in the payload of the request. This example is sourced from the Payment Initiation API Specification

POST /payment-submissions HTTP/1.1
Authorization: Bearer SlAV32hkKG
x-idempotency-key: FRESNO.1317.GFX.22
x-fapi-financial-id: OB/2017/001
x-fapi-customer-last-logged-time: 2017-06-13T11:36:09
x-fapi-customer-ip-address: 104.25.212.99
x-fapi-interaction-id: 93bac548-d2de-4546-b106-880a5018460d
Content-Type: application/json
Accept: application/json
 
{
  "Data": {
    "PaymentId": "58923",
    "Initiation": {
      "InstructionIdentification": "ACME412",
      "EndToEndIdentification": "FRESCO.21302.GFX.20",
      "InstructedAmount": {
        "Amount": "165.88",
        "Currency": "GBP"
      },
      "CreditorAccount": {
        "SchemeName": "SortCodeAccountNumber",
        "Identification": "08080021325698",
        "Name": "ACME Inc",
        "SecondaryIdentification": "0002"
      },
      "RemittanceInformation": {
        "Reference": "FRESCO-101",
        "Unstructured": "Internal ops code 5120101"
      }
    }
  },
  "Risk": {
    "PaymentContextCode": "EcommerceGoods",
    "MerchantCategoryCode": "5967",
    "MerchantCustomerIdentification": "053598653254",
    "DeliveryAddress": {
      "AddressLine": [
        "Flat 7",
        "Acacia Lodge"
      ],
      "StreetName": "Acacia Avenue",
      "BuildingNumber": "27",
      "PostCode": "GU31 2ZZ",
      "TownName": "Sparsholt",
      "CountySubDivision": [
        "Wessex"
      ],
      "Country": "UK"
    }
  }
}

HTTP/1.1 201 Created
x-fapi-interaction-id: 93bac548-d2de-4546-b106-880a5018460d
Content-Type: application/json
 
{
  "Data": {
    "PaymentSubmissionId": "58923-001",
    "PaymentId": "58923",
    "Status": "AcceptedSettlementInProcess",
    "CreationDateTime": "2017-06-05T15:15:22+00:00"
  },
  "Links": {
    "Self": "https://api.alphabank.com/open-banking/v1.0/payment-submissions/58923-001"
  },
  "Meta": {}
}

Step 5 - Get Payment-Submission Status

1. The PISP can query for the status of a Payment-Submission by invoking the /payment-submissions using the known PaymentSubmissionId. This can use an existing access token with payments scope or the PISP can obtain a fresh access token by replaying the client credentials grant request as per Step 2 - Setup Single Payment Initiation.

GET /payment-submissions/58923-001 HTTP/1.1
Authorization: Bearer SlAV32hkKG
x-fapi-financial-id: OB/2017/001
x-fapi-customer-last-logged-time: 2017-06-13T11:36:09
x-fapi-customer-ip-address: 104.25.212.99
x-fapi-interaction-id: 93bac548-d2de-4546-b106-880a5018460d
Accept: application/json

HTTP/1.1 200 OK
x-fapi-interaction-id: 93bac548-d2de-4546-b106-880a5018460d
Content-Type: application/json
 
{
  "Data": {
    "PaymentSubmissionId": "58923-001",
    "PaymentId": "58923",
    "Status": "AcceptedSettlementInProcess",
    "CreationDateTime": "2017-06-05T15:15:22+00:00"
  },
  "Links": {
    "Self": "https://api.alphabank.com/open-banking/v1.0/payment-submissions/58923-001"
  },
  "Meta": {}
}

2. A PISP can also optionally query for the status of a Payment resource by invoking /payments/{PaymentId}. This can use an existing access token with payments scope or the PISP can obtain a fresh access token by replaying the client credentials grant request as per Step 2 - Setup Single Payment Initiation.

Account API Specification

The sequence diagram below highlights the OAuth 2.0 Client Credentials Grant and OIDC Hybrid flow that are used by the Account and Transactions API.

participant PSU
participant AISP
participant ASPSP Authorisation Server
participant ASPSP Resource Server
autonumber 1
      
PSU -> AISP: Establish TLS 1.2
    
      
note over PSU, ASPSP Resource Server
    Step 1: Request account information
end note
PSU -> AISP: Get account/transaction information
     
note over PSU, ASPSP Resource Server
    Step 2: Setup account request
end note
AISP <-> ASPSP Authorisation Server: Establish TLS 1.2 MA
    
    note left of AISP
        Client Credentials Grant
    end note
    AISP->ASPSP Authorisation Server: POST /token (client authentication credentials, scope:accounts)
    ASPSP Authorisation Server->ASPSP Authorisation Server: Validate client authentication credentials, scope
    ASPSP Authorisation Server->ASPSP Authorisation Server: Validate clientId matches client SSL cert
    ASPSP Authorisation Server -> AISP: HTTP 200 (OK) access-token (scope:accounts)
    
    
AISP <-> ASPSP Resource Server: Establish TLS 1.2 MA
AISP -> ASPSP Resource Server: POST /account-requests (access-token - scope:accounts)
    ASPSP Resource Server->ASPSP Resource Server: Validate access token
    ASPSP Resource Server->ASPSP Resource Server: Validate scope:accounts
    ASPSP Resource Server->ASPSP Resource Server: Validate clientId matches client SSL cert
    ASPSP Resource Server->ASPSP Resource Server: Create new account resource
    ASPSP Resource Server->ASPSP Resource Server: Bind AccountRequestId with ClientId
    
ASPSP Resource Server -> AISP: HTTP 201 (Created), AccountRequestId
    note right of AISP
        Begin OIDC Hybrid Flow.
        See 6.1.  Passing a Request Object by Value
        See 5.5.  Requesting Claims using the "claims" Request Parameter
        The claims parameter must at least request:
             "id_token": {
       "openbanking_intent_id": {"value": AccountRequestId, "essential": true},
       "acr": {"essential": true}
      }
      The response object must be signed using the PISP's private key.
    end note
    AISP->AISP: Persist AccountRequestId
      note right of AISP
        The AISP should store the AccountRequestId in a manner
        that it can be retrieved again later in the flow in Step 4.
             
        This could be stored in the user session (and retrieved using 'state'
        as a key) or the PSU could use some other unique identifier.
             
        This can be re-retrieved in [81] and [96].
             
    end note
    
    AISP->AISP: Create signed request object with requested Claims (AccountRequestId)
        
    
    
    AISP -> PSU: HTTP 302 (Found); Location: /authorize,\nredirect-uri, clientId, state, nonce, scope=openid accounts,\nresponse-type=code id_token,\nrequest=signed JWT request object - AccountRequestId)
    
     
note over PSU, ASPSP Resource Server
Step 3: Authorise consent
end note
PSU -> ASPSP Authorisation Server: HTTP GET /authorize redirect-uri, clientId, state, nonce, scope=openid accounts, response-type=code id_token,\nrequest=signed JWT request object - AccountRequestId
ASPSP Authorisation Server->ASPSP Authorisation Server: Validate clientid, scope
ASPSP Authorisation Server->ASPSP Authorisation Server: Validate redirect-uri for clientId
ASPSP Authorisation Server->ASPSP Authorisation Server: Validate JWT request claim -AccountRequestId
note right of ASPSP Authorisation Server
        Validate the request object by using the PISP's public key.
        PISP certificate will be identified using the kid claim
        in the JOSE header of the request object.
             
        Check that the AccountRequestId belongs to the ClientId that initiated the request.
    end note
    
PSU <-> ASPSP Authorisation Server: Authenticate (Login and Consent Page)
PSU <-> ASPSP Authorisation Server: SCA if required
PSU <-> ASPSP Authorisation Server: Select Accounts
ASPSP Authorisation Server->ASPSP Authorisation Server: Generate authorization-code, id_token
note right of ASPSP Authorisation Server
    id_token claims:{
    c_hash: 123,
    s_hash: 456
    }
    id_token must be signed using the ASPSP's private key.
    The generation of c_hash is documented in OIDC: 3.3.2.11.  ID Token
    The generation of s_hash is in FAPI R/W spec: Section 5.1
    http://openid.net/specs/openid-financial-api-part-2-wd-02.html#introduction
end note
ASPSP Authorisation Server-> ASPSP Authorisation Server: Bind selected Accounts to AccountRequestId
ASPSP Authorisation Server -> PSU: HTTP 302 (Found); Location: redirect-uri (authorization-code, id_token, state)
PSU -> AISP: HTTP GET redirect-uri (authorization-code, id_token, state)
AISP->AISP: Validate signature on id_token
note right of AISP
    Validate the id_token by using the ASPSP's public key.
    ASPSP certificate will be identified using the kid claim
    in the JOSE header of the id_token
end note
AISP->AISP: Validate authorization-code using id_token (c_hash)
AISP->AISP: Validate state using id_token (s_hash)
AISP->AISP: Validate nonce using id_token
note right of AISP:
    Exchange authorization-code for access token.
end note
    
    
    
AISP <-> ASPSP Authorisation Server: Establish TLS 1.2 MA
AISP -> ASPSP Authorisation Server: HTTP POST /token (client authentication credentials,\nauthorization-code, grant_type, redirect_uri)
    ASPSP Authorisation Server->ASPSP Authorisation Server: Validate clientId matches client SSL cert
    ASPSP Authorisation Server->ASPSP Authorisation Server: Validate client authentication credentials,\nauthorization-code
    ASPSP Authorisation Server->ASPSP Authorisation Server: Generate access-token
    ASPSP Authorisation Server->ASPSP Authorisation Server: Bind access-token to AccountRequestId
    note right of ASPSP Authorisation Server
        Implies an association of Accounts to access-token
    end note
    ASPSP Authorisation Server->ASPSP Resource Server: Update account-requests Status to Authorised
    ASPSP Resource Server->ASPSP Authorisation Server:OK
    note right of ASPSP Authorisation Server
        Implementation of how the resource is updated is ASPSP specific (There
        is no standardised API for this)
    end note
alt Access Token
    ASPSP Authorisation Server -> AISP: HTTP 200 (OK) access-token (scope:accounts)
  
else Optional Refresh Token
    ASPSP Authorisation Server->ASPSP Authorisation Server: Generate Refresh Token
    ASPSP Authorisation Server -> AISP: HTTP 200 (OK) access-token, refresh-token (scope:accounts)
  
end
     
      
note over PSU, ASPSP Resource Server
Step 4: Request data
end note
AISP <-> ASPSP Resource Server: Establish TLS 1.2 MA
AISP<->AISP: Retrieve access-token
note left of AISP
    Retrieve the access-token that was issued in Step [42].
    The access-token is  linked with consented Accounts
    from Steps [27] and [39]
end note
  
alt Valid Access Token
    AISP -> ASPSP Resource Server: GET /accounts (access-token - scope:accounts)
    ASPSP Resource Server->ASPSP Resource Server: Validate access-token
    ASPSP Resource Server->ASPSP Resource Server: Validate access-token matches client SSL cert
    ASPSP Resource Server->ASPSP Resource Server: Validate scope:accounts
    ASPSP Resource Server -> AISP: HTTP 200 (OK), List of accounts containing AccountId(s)
    AISP -> ASPSP Resource Server: GET /accounts/{AccountId}/transactions (access-token - scope:accounts)
    ASPSP Resource Server->ASPSP Resource Server: Validate access-token
    ASPSP Resource Server->ASPSP Resource Server: Validate access-token matches client SSL cert
 
    ASPSP Resource Server->ASPSP Resource Server: Validate scope:accounts
    ASPSP Resource Server->ASPSP Resource Server: Validate access-token bound to AccountId
    ASPSP Resource Server -> AISP: HTTP 200 (OK), List of transactions
else Expired Access Token
    AISP->AISP: Retrieve Refresh Token from [44]
    AISP->ASPSP Authorisation Server:HTTP POST /token (client authentication credentials,\ngrant_type=refresh_token,refresh_token=[58],\nscope=openid accounts)
    ASPSP Authorisation Server->ASPSP Authorisation Server: Validate clientId matches client SSL cert
    ASPSP Authorisation Server->ASPSP Authorisation Server: Validate client authentication credentials,\refresh_token
    ASPSP Authorisation Server->ASPSP Authorisation Server: Generate Access Token and Refresh Token
    ASPSP Authorisation Server -> AISP: HTTP 200 (OK) access-token, refresh-token (scope:accounts)
    AISP -> ASPSP Resource Server: GET /accounts (access-token - scope:accounts)
    ASPSP Resource Server->ASPSP Resource Server: Validate access-token
    ASPSP Resource Server->ASPSP Resource Server: Validate access-token matches client SSL cert
    ASPSP Resource Server->ASPSP Resource Server: Validate scope:accounts
    ASPSP Resource Server -> AISP: HTTP 200 (OK), List of accounts containing AccountId(s)
    AISP -> ASPSP Resource Server: GET /accounts/{AccountId}/transactions (access-token - scope:accounts)
    ASPSP Resource Server->ASPSP Resource Server: Validate access-token
    ASPSP Resource Server->ASPSP Resource Server: Validate access-token matches client SSL cert
    ASPSP Resource Server->ASPSP Resource Server: Validate scope:accounts
    ASPSP Resource Server->ASPSP Resource Server: Validate access-token bound to AccountId
    ASPSP Resource Server -> AISP: HTTP 200 (OK), List of transactions
else Account Request - Get Status
AISP <-> ASPSP Authorisation Server: Establish TLS 1.2 MA
    
    note left of AISP
        Client Credentials Grant
    end note
    AISP->ASPSP Authorisation Server: POST /token (client authentication credentials, scope:accounts)
    ASPSP Authorisation Server->ASPSP Authorisation Server: Validate client authentication credentials, scope
    ASPSP Authorisation Server->ASPSP Authorisation Server: Validate clientId matches client SSL cert
    ASPSP Authorisation Server -> AISP: HTTP 200 (OK) access-token (scope:accounts)
    
    
    AISP <-> ASPSP Resource Server: Establish TLS 1.2 MA
    AISP->AISP: Retrieve AccountRequestId from [16]
    AISP -> ASPSP Resource Server: GET /account-requests/{AccountRequestId} (access-token - scope:accounts)
        ASPSP Resource Server->ASPSP Resource Server: Validate access token
        ASPSP Resource Server->ASPSP Resource Server: Validate scope:accounts
        ASPSP Resource Server->ASPSP Resource Server: Validate clientId matches client SSL cert
        ASPSP Resource Server->ASPSP Resource Server: Lookup AccountRequestId resource
     
    ASPSP Resource Server -> AISP: HTTP 200 (OK), AccountRequest Status
 
else Account Request- PSU removes consent at a later point in time with the AISP
PSU -> AISP: Establish TLS 1.2
PSU -> AISP: Remove Consent
 
AISP <-> ASPSP Authorisation Server: Establish TLS 1.2 MA
    
    note left of AISP
        Client Credentials Grant
    end note
    AISP->ASPSP Authorisation Server: POST /token (client authentication credentials, scope:accounts)
    ASPSP Authorisation Server->ASPSP Authorisation Server: Validate client authentication credentials, scope
    ASPSP Authorisation Server->ASPSP Authorisation Server: Validate clientId matches client SSL cert
    ASPSP Authorisation Server -> AISP: HTTP 200 (OK) access-token (scope:accounts)
    
    
    AISP <-> ASPSP Resource Server: Establish TLS 1.2 MA
    AISP->AISP: Retrieve AccountRequestId from [16]
    AISP -> ASPSP Resource Server: DELETE /account-requests/{AccountRequestId} (access-token - scope:accounts)
        ASPSP Resource Server->ASPSP Resource Server: Validate access token
        ASPSP Resource Server->ASPSP Resource Server: Validate scope:accounts
        ASPSP Resource Server->ASPSP Resource Server: Validate clientId matches client SSL cert
        ASPSP Resource Server->ASPSP Resource Server: Delete AccountRequestId resource
     
    ASPSP Resource Server -> AISP: HTTP 204 (No Content)
    AISP->PSU: Consent Removed
end

Client Credentials Grant Type (OAuth 2.0)

Summary

This grant type is used by the AISP in Step 2 to register an intent for the PSU to allow the AISP to retrieve their Account information from an ASPSP.

1. The AISP initiates an Authorization request using valid Client Credentials Grant type and scope(s)
2. The ASPSP Authorization Server validates the Client Authentication request from the AISP and generates an Access Token response where the request is valid
3. The AISP uses the Access Token to create a new Account Request resource against the ASPSP Resource Server
4. The ASPSP Resource server responds with the AccountRequestId representing the resource it has created. 

OIDC Hybrid Flow

Summary

• This is initiated at the end of Step 2 by the AISP after the AccountRequestId is generated by the ASPSP and returned to the AISP.
• This is used in a redirect across the PSU and ASPSP in Step 3 in order for the PSU to authorize consent with the ASPSP - for the AISP to proceed with the requesting Account information.
• This is used across the AISP and ASPSP in Step 4 by swapping the Authorization Code for an Access Token in order to retrieve PSU Account information.

Non-Normative HTTP Request and Response Examples

Step 1 - Request Account Information

There are no Requests and Responses against the Payments API in this Step for the PSU, PISP and ASPSP.

Step 2 - Setup Account Request

1. AISP obtains an Access Token using a Client Credentials Grant Type. The scope accounts must be used. When an Access Token expires, the AISP will need to re-request for another Access Token using the same request below.

POST  /as/token.oauth2 HTTP/1.1
Host: https://authn.alphabank.com
Content-Type: application/x-www-form-urlencoded
Accept: application/json
grant_type=client_credentials
&scope=accounts
&client-assertion-type%3Ajwt-bearer
&client_assertion=eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9.eyJpc3MiOiJodHRw
czovL2p3dC1pZHAuZXhhbXBsZS5jb20iLCJzdWIiOiJtYWlsdG86bWlrZUBleGFtcGxlLmN
vbSIsIm5iZiI6MTQ5OTE4MzYwMSwiZXhwIjoxNDk5MTg3MjAxLCJpYXQiOjE0OTkxODM2MD
EsImp0aSI6ImlkMTIzNDU2IiwidHlwIjoiaHR0cHM6Ly9leGFtcGxlLmNvbS9yZWdpc3Rlc
iJ9.SAxPMaJK_wYl_W2idTQASjiEZ4UoI7-P2SbmnHKr6LvP8ZJZX6JlnpK_xClJswAni1T
p1UnHJslc08JrexctaeEIBrqwHG18iBcWKjhHK2Tv5m4nbTsSi1MFQOlMUTRFq3_LQiHqV2
M8Hf1v9q9YaQqxDa4MK0asDUtE_zYMHz8kKDb-jj-Vh4mVDeM4_FPiffd2C5ckjkrZBNOK0
01Xktm7xTqX6fk56KTrejeA4x6D_1ygJcGfjZCv6Knki7Jl-6MfwUKb9ZoZ9LiwHf5lLXPuy
_QrOyM0pONWKj9K4Mj7I4GPGvzyVqpaZUgjcOaZY_rlu_p9tnSlE781dDLuw

{
  "alg": "RS256",
  "typ": "JWT",
  "kid": "1234adsf"
}
.
{
  "iss": "s6BhdRkqt3",
  "sub": "s6BhdRkqt3",
  "exp": 1499187201,
  "iat": 1499183601,
  "jti": "id123456",
  "aud": "https://authn.alphabank.com/as/token.oauth2"
}
.
<<signature>>

Content-Length: 1103
Content-Type: application/json
Date: Mon, 26 Jun 2017 15:18:28 GMT
{
    "access_token": "2YotnFZFEjr1zCsicMWpAA",
    "expires_in": 3600,
    "token_type": "bearer",
	"scope":"accounts"
}

2. AISP uses the Access Token (with accounts scope) from the ASPSP to invoke the Accounts API.  This example is sourced directly from the Account and Transactions API Specification

POST /account-requests HTTP/1.1
Authorization: Bearer 2YotnFZFEjr1zCsicMWpAA
x-fapi-financial-id: OB/2017/001
x-fapi-customer-last-logged-time: 2017-06-13T11:36:09
x-fapi-customer-ip-address: 104.25.212.99
x-fapi-interaction-id: 93bac548-d2de-4546-b106-880a5018460d
Content-Type: application/json
Accept: application/json

{
  "Data": {
    "Permissions": [
      "ReadAccountsDetail",
      "ReadBalances",
      "ReadBeneficiariesDetail",
      "ReadDirectDebits",
      "ReadProducts",
      "ReadStandingOrdersDetail",
      "ReadTransactionsCredits",
      "ReadTransactionsDebits",
      "ReadTransactionsDetail"
    ],
    "ExpirationDateTime": "2017-05-02T00:00:00+00:00",
    "TransactionFromDateTime": "2017-05-03T00:00:00+00:00",
    "TransactionToDateTime": "2017-12-03T00:00:00+00:00"
  },
  "Risk": {}
}

HTTP/1.1 201 Created
x-fapi-interaction-id: 93bac548-d2de-4546-b106-880a5018460d
Content-Type: application/json
 
{
  "Data": {
    "AccountRequestId": "88379",
    "Status": "AwaitingAuthorisation",
    "CreationDateTime": "2017-05-02T00:00:00+00:00",
    "Permissions": [
      "ReadAccountsDetail",
      "ReadBalances",
      "ReadBeneficiariesDetail",
      "ReadDirectDebits",
      "ReadProducts",
      "ReadStandingOrdersDetail",
      "ReadTransactionsCredits",
      "ReadTransactionsDebits",
      "ReadTransactionsDetail"
    ],
    "ExpirationDateTime": "2017-08-02T00:00:00+00:00",
    "TransactionFromDateTime": "2017-05-03T00:00:00+00:00",
    "TransactionToDateTime": "2017-12-03T00:00:00+00:00"
  },
  "Risk": {},
  "Links": {
    "Self": "/account-requests/88379"
  },
  "Meta": {
    "TotalPages": 1
  }
}

Step 3 - Authorize Consent

1. AISP receives a AccountRequestId from the ASPSP. The AISP then creates an Authorization request (using a signed JWT Request containing the AccountRequestId as a claim) for the PSU to consent to the Account request directly with their ASPSP. The request is an OIDC Hybrid flow (requesting for Code and id_token)

HTTP/1.1 302 Found
  Location: https://api.mytpp.com/cb#
    code=SplxlOBeZQQYbYS6WxSbIA
    &id_token=eyJ0 ... NiJ9.eyJ1c ... I6IjIifX0.DeWt4Qu ... ZXso
    &state=af0ifjsldkj

2. The PSU is then redirected to the AISP. The AISP will now possess the Authorization Code and ID Token from the ASPSP. Note at this point, there is no Access Token. The AISP will now introspect the ID Token and use it as a detached signature to check:

• The hash of the Authorization Code to prove it hasn't been tampered with during redirect (comparing the hash value against the c_hash attribute in ID Token)
• The hash of the State to prove it hasn't been tampered with during redirect (comparing the state hash value against the s_hash attribute in the ID Token)

3. Once the state and code validations have been confirmed as successful by use of the ID token, the AISP will proceed to obtain an Access Token from the ASPSP using the Authorization Code they now possess. The AISP will present its Authorization Code together with the private_key_jwt. The Access Token is required by the AISP in order to access PSU Account information. The accounts scope should already be associated with the Authorization Code generated in the previous step.

POST  /as/token.oauth2 HTTP/1.1
Host: https://authn.alphabank.com
Content-Type: application/x-www-form-urlencoded
Accept: application/json
grant_type=authorization_code
&redirect_uri=https://api.mytpp.com/cb
&code=SplxlOBeZQQYbYS6WxSbIA
&client-assertion-type%3Ajwt-bearer
&client_assertion=eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9.eyJpc3MiOiJodHRw
czovL2p3dC1pZHAuZXhhbXBsZS5jb20iLCJzdWIiOiJtYWlsdG86bWlrZUBleGFtcGxlLmN
vbSIsIm5iZiI6MTQ5OTE4MzYwMSwiZXhwIjoxNDk5MTg3MjAxLCJpYXQiOjE0OTkxODM2MD
EsImp0aSI6ImlkMTIzNDU2IiwidHlwIjoiaHR0cHM6Ly9leGFtcGxlLmNvbS9yZWdpc3Rlc
iJ9.SAxPMaJK_wYl_W2idTQASjiEZ4UoI7-P2SbmnHKr6LvP8ZJZX6JlnpK_xClJswAni1T
p1UnHJslc08JrexctaeEIBrqwHG18iBcWKjhHK2Tv5m4nbTsSi1MFQOlMUTRFq3_LQiHqV2
M8Hf1v9q9YaQqxDa4MK0asDUtE_zYMHz8kKDb-jj-Vh4mVDeM4_FPiffd2C5ckjkrZBNOK0
01Xktm7xTqX6fk56KTrejeA4x6D_1ygJcGfjZCv6Knki7Jl-6MfwUKb9ZoZ9LiwHf5lLXPuy
_QrOyM0pONWKj9K4Mj7I4GPGvzyVqpaZUgjcOaZY_rlu_p9tnSlE781dDLuw

{
  "alg": "RS256",
  "kid": "12345",
  "typ": "JWT"
}
.
{
  "iss": "s6BhdRkqt3",
  "sub": "s6BhdRkqt3",
  "exp": 1499187201,
  "iat": 1499183601,
  "jti": "id123456",
  "aud": "https://authn.alphabank.com/as/token.oauth2"
}
.
<<signature>>

HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
Pragma: no-cache
 
{
 "access_token": "SlAV32hkKG",
 "token_type": "Bearer",
 "expires_in": 3600,
 "refresh_token": "1Sm4HAl33z4"
}

Step 4 - Request Account Data

1. The AISP can use the Access Token to retrieve Accounts (bulk or specific). The following examples are from the Account and Transaction API Specification

Where the initial Access Token expires, the AISP can use the Refresh token in order to obtain a fresh Access Token.

GET /accounts HTTP/1.1
Authorization: Bearer SlAV32hkKG
x-fapi-financial-id: OB/2017/001
x-fapi-customer-last-logged-time: 2017-06-13T11:36:09
x-fapi-customer-ip-address: 104.25.212.99
x-fapi-interaction-id: 93bac548-d2de-4546-b106-880a5018460d
Accept: application/json

HTTP/1.1 200 OK
x-fapi-interaction-id: 93bac548-d2de-4546-b106-880a5018460d
Content-Type: application/json
 
{
  "Data": {
    "Account": [
      {
        "AccountId": "22289",
        "Currency": "GBP",
        "Nickname": "Bills",
        "Account": {
          "SchemeName": "SortCodeAccountNumber",
          "Identification": "80200110203345",
          "Name": "Mr Kevin",
          "SecondaryIdentification": "00021"
        }
      },
      {
        "AccountId": "31820",
        "Currency": "GBP",
        "Nickname": "Household",
        "Account": {
          "SchemeName": "SortCodeAccountNumber",
          "Identification": "80200110203348",
          "Name": "Mr Kevin"
        }
      }
    ]
  },
  "Links": {
    "Self": "/accounts/"
  },
  "Meta": {
    "TotalPages": 1
  }
}

GET /accounts/22289 HTTP/1.1
Authorization: Bearer SlAV32hkKG
x-fapi-financial-id: OB/2017/001
x-fapi-customer-last-logged-time: 2017-06-13T11:36:09
x-fapi-customer-ip-address: 104.25.212.99
x-fapi-interaction-id: 93bac548-d2de-4546-b106-880a5018460d
Accept: application/json

HTTP/1.1 200 OK
x-fapi-interaction-id: 93bac548-d2de-4546-b106-880a5018460d
Content-Type: application/json
 
{
  "Data": {
    "Account": [
      {
        "AccountId": "22289",
        "Currency": "GBP",
        "Nickname": "Bills",
        "Account": {
          "SchemeName": "SortCodeAccountNumber",
          "Identification": "80200110203345",
          "Name": "Mr Kevin",
          "SecondaryIdentification": "00021"
        }
      }
    ]
  },
  "Links": {
    "Self": "/accounts/22289"
  },
  "Meta": {
    "TotalPages": 1
  }
}

POST  /as/token.oauth2 HTTP/1.1
Host: https://authn.alphabank.com
Content-Type: application/x-www-form-urlencoded
Accept: application/json
grant_type=refresh_token
&refresh_token=1Sm4HAl33z4
&scope=openid accounts
&client-assertion-type%3Ajwt-bearer
&client_assertion=eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9.eyJpc3MiOiJodHRw
czovL2p3dC1pZHAuZXhhbXBsZS5jb20iLCJzdWIiOiJtYWlsdG86bWlrZUBleGFtcGxlLmN
vbSIsIm5iZiI6MTQ5OTE4MzYwMSwiZXhwIjoxNDk5MTg3MjAxLCJpYXQiOjE0OTkxODM2MD
EsImp0aSI6ImlkMTIzNDU2IiwidHlwIjoiaHR0cHM6Ly9leGFtcGxlLmNvbS9yZWdpc3Rlc
iJ9.SAxPMaJK_wYl_W2idTQASjiEZ4UoI7-P2SbmnHKr6LvP8ZJZX6JlnpK_xClJswAni1T
p1UnHJslc08JrexctaeEIBrqwHG18iBcWKjhHK2Tv5m4nbTsSi1MFQOlMUTRFq3_LQiHqV2
M8Hf1v9q9YaQqxDa4MK0asDUtE_zYMHz8kKDb-jj-Vh4mVDeM4_FPiffd2C5ckjkrZBNOK0
01Xktm7xTqX6fk56KTrejeA4x6D_1ygJcGfjZCv6Knki7Jl-6MfwUKb9ZoZ9LiwHf5lLXPuy
_QrOyM0pONWKj9K4Mj7I4GPGvzyVqpaZUgjcOaZY_rlu_p9tnSlE781dDLuw

HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
Pragma: no-cache
 
{
 "access_token": "TYstftas123j",
 "token_type": "Bearer",
 "expires_in": 3600,
 "refresh_token": "XUUGas123ed"
}

Edge Cases

This section provides further information on potential edge cases that may arise via the implementation of Accounts and Payments API Specifications. 

PSU Consent Authorization Interrupt with ASPSP